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All the ideas for 'The Evolution of Logic', 'Principles of Philosophy of the Future' and 'Existentialism: an introduction'

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77 ideas

1. Philosophy / C. History of Philosophy / 4. Later European Philosophy / c. Eighteenth century philosophy
We are all post-Kantians, because he set the current agenda for philosophy [Hart,WD]
     Full Idea: We are all post-Kantians, ...because Kant set an agenda for philosophy that we are still working through.
     From: William D. Hart (The Evolution of Logic [2010], 2)
     A reaction: Hart says that the main agenda is set by Kant's desire to defend the principle of sufficient reason against Hume's attack on causation. I would take it more generally to be the assessment of metaphysics, and of a priori knowledge.
1. Philosophy / D. Nature of Philosophy / 5. Aims of Philosophy / b. Philosophy as transcendent
Only that which can be an object of religion is an object of philosophy [Feuerbach]
     Full Idea: Only that which can be an object of religion is an object of philosophy.
     From: Ludwig Feuerbach (Principles of Philosophy of the Future [1843], §35)
     A reaction: The temple of Pythagoras at Solon sounds like an embodiment of this idea. The obvious candidate would be truth, to which philosophers must show almost religious respect. Some what motivates the philosophy of a minimalist (Idea 3750)?
1. Philosophy / D. Nature of Philosophy / 5. Aims of Philosophy / d. Philosophy as puzzles
The problems are the monuments of philosophy [Hart,WD]
     Full Idea: The real monuments of philosophy are its problems.
     From: William D. Hart (The Evolution of Logic [2010], 2)
     A reaction: Presumably he means '....rather than its solutions'. No other subject would be very happy with that sort of claim. Compare Idea 8243. A complaint against analytic philosophy is that it has achieved no consensus at all.
1. Philosophy / F. Analytic Philosophy / 5. Linguistic Analysis
Philosophy should not focus on names, but on the determined nature of things [Feuerbach]
     Full Idea: Philosophy need not care about the conceptions that common usage or misuse attaches to a name; philosophy, however, has to bind itself to the determined nature of things, whose signs are names.
     From: Ludwig Feuerbach (Principles of Philosophy of the Future [1843], §23)
     A reaction: I like this attempt to nip ordinary language philosophy in the bud. Indeed I like the notion of philosophy binding itself to the 'determined nature of things' (which sound like essences to me), rather than to their names or descriptions.
1. Philosophy / F. Analytic Philosophy / 6. Logical Analysis
To study abstract problems, some knowledge of set theory is essential [Hart,WD]
     Full Idea: By now, no education in abstract pursuits is adequate without some familiarity with sets.
     From: William D. Hart (The Evolution of Logic [2010], 10)
     A reaction: A heart-sinking observation for those who aspire to study metaphysics and modality. The question is, what will count as 'some' familiarity? Are only professional logicians now allowed to be proper philosophers?
1. Philosophy / H. Continental Philosophy / 1. Continental Philosophy
Modern philosophy begins with Descartes' abstraction from sensation and matter [Feuerbach]
     Full Idea: The beginning of Descartes' philosophy, namely, the abstraction from sensation and matter, is the beginning of modern speculative philosophy.
     From: Ludwig Feuerbach (Principles of Philosophy of the Future [1843], §10)
     A reaction: In Britain it might be said that modern philosophy begins with a rebellion against Descartes' move. Feuerbach is charting the movement towards idealism.
Empiricism is right about ideas, but forgets man himself as one of our objects [Feuerbach]
     Full Idea: Empiricism rightly derives the origin of our ideas from the senses; only it forgets that the most important and essential object of man is man himself.
     From: Ludwig Feuerbach (Principles of Philosophy of the Future [1843], §41)
     A reaction: This seems to nicely pinpoint the objection of most 'continental' philosophy to British empiricism and analytic philosophy. It seems to point towards Husserl's phenomenology as the next step. It is true that empiricists divided person from world.
1. Philosophy / H. Continental Philosophy / 2. Phenomenology
Phenomenologists say all experience is about something and is directed [Aho]
     Full Idea: Phenomenologists agree that all experience has an intentional structure, that is, my experience is always about or of something; it is always directed towards an object.
     From: Kevin Aho (Existentialism: an introduction [2014], 2 'Phenomenology')
     A reaction: I am just beginning to grasp that the analytic debates about perception are a re-enactment of the Kantian debates about the thing-in-itself. This is the sort of idea you find in McDowell. Presumably the idea denies the Given, and raw sense-data.
2. Reason / B. Laws of Thought / 1. Laws of Thought
The laws of reality are also the laws of thought [Feuerbach]
     Full Idea: The laws of reality are also the laws of thought.
     From: Ludwig Feuerbach (Principles of Philosophy of the Future [1843], §45)
     A reaction: I like this a lot, though it runs contrary to a lot of conventionalist thinking in the twentieth century. Russell, though, agrees with Feuerbach (Idea 5405). There is not much point to thought if it doesn't plug into reality at the roots.
3. Truth / C. Correspondence Truth / 2. Correspondence to Facts
Tarski showed how we could have a correspondence theory of truth, without using 'facts' [Hart,WD]
     Full Idea: It is an ancient and honourable view that truth is correspondence to fact; Tarski showed us how to do without facts here.
     From: William D. Hart (The Evolution of Logic [2010], 2)
     A reaction: This is a very interesting spin on Tarski, who certainly seems to endorse the correspondence theory, even while apparently inventing a new 'semantic' theory of truth. It is controversial how far Tarski's theory really is a 'correspondence' theory.
3. Truth / F. Semantic Truth / 1. Tarski's Truth / b. Satisfaction and truth
Truth for sentences is satisfaction of formulae; for sentences, either all sequences satisfy it (true) or none do [Hart,WD]
     Full Idea: We explain truth for sentences in terms of satisfaction of formulae. The crux here is that for a sentence, either all sequences satisfy it or none do (with no middle ground). For formulae, some sequences may satisfy it and others not.
     From: William D. Hart (The Evolution of Logic [2010], 4)
     A reaction: This is the hardest part of Tarski's theory of truth to grasp.
3. Truth / F. Semantic Truth / 2. Semantic Truth
A first-order language has an infinity of T-sentences, which cannot add up to a definition of truth [Hart,WD]
     Full Idea: In any first-order language, there are infinitely many T-sentences. Since definitions should be finite, the agglomeration of all the T-sentences is not a definition of truth.
     From: William D. Hart (The Evolution of Logic [2010], 4)
     A reaction: This may be a warning shot aimed at Davidson's extensive use of Tarski's formal account in his own views on meaning in natural language.
4. Formal Logic / B. Propositional Logic PL / 2. Tools of Propositional Logic / c. Derivation rules of PL
Conditional Proof: infer a conditional, if the consequent can be deduced from the antecedent [Hart,WD]
     Full Idea: A 'conditional proof' licenses inferences to a conditional from a deduction of its consequent from its antecedent.
     From: William D. Hart (The Evolution of Logic [2010], 4)
     A reaction: That is, a proof can be enshrined in an arrow.
4. Formal Logic / C. Predicate Calculus PC / 2. Tools of Predicate Calculus / e. Existential quantifier ∃
∃y... is read as 'There exists an individual, call it y, such that...', and not 'There exists a y such that...' [Hart,WD]
     Full Idea: When a quantifier is attached to a variable, as in '∃(y)....', then it should be read as 'There exists an individual, call it y, such that....'. One should not read it as 'There exists a y such that...', which would attach predicate to quantifier.
     From: William D. Hart (The Evolution of Logic [2010], 4)
     A reaction: The point is to make clear that in classical logic the predicates attach to the objects, and not to some formal component like a quantifier.
4. Formal Logic / F. Set Theory ST / 1. Set Theory
Set theory articulates the concept of order (through relations) [Hart,WD]
     Full Idea: It is set theory, and more specifically the theory of relations, that articulates order.
     From: William D. Hart (The Evolution of Logic [2010])
     A reaction: It would seem that we mainly need set theory in order to talk accurately about order, and about infinity. The two come together in the study of the ordinal numbers.
Nowadays ZFC and NBG are the set theories; types are dead, and NF is only useful for the whole universe [Hart,WD]
     Full Idea: The theory of types is a thing of the past. There is now nothing to choose between ZFC and NBG (Neumann-Bernays-Gödel). NF (Quine's) is a more specialized taste, but is a place to look if you want the universe.
     From: William D. Hart (The Evolution of Logic [2010], 3)
4. Formal Logic / F. Set Theory ST / 2. Mechanics of Set Theory / a. Symbols of ST
∈ relates across layers, while ⊆ relates within layers [Hart,WD]
     Full Idea: ∈ relates across layers (Plato is a member of his unit set and the set of people), while ⊆ relates within layers (the singleton of Plato is a subset of the set of people). This distinction only became clear in the 19th century.
     From: William D. Hart (The Evolution of Logic [2010], 1)
     A reaction: Getting these two clear may be the most important distinction needed to understand how set theory works.
4. Formal Logic / F. Set Theory ST / 3. Types of Set / b. Empty (Null) Set
Without the empty set we could not form a∩b without checking that a and b meet [Hart,WD]
     Full Idea: Without the empty set, disjoint sets would have no intersection, and we could not form a∩b without checking that a and b meet. This is an example of the utility of the empty set.
     From: William D. Hart (The Evolution of Logic [2010], 1)
     A reaction: A novice might plausibly ask why there should be an intersection for every pair of sets, if they have nothing in common except for containing this little puff of nothingness. But then what do novices know?
4. Formal Logic / F. Set Theory ST / 4. Axioms for Sets / i. Axiom of Foundation VIII
In the modern view, foundation is the heart of the way to do set theory [Hart,WD]
     Full Idea: In the second half of the twentieth century there emerged the opinion that foundation is the heart of the way to do set theory.
     From: William D. Hart (The Evolution of Logic [2010], 3)
     A reaction: It is foundation which is the central axiom of the iterative conception of sets, where each level of sets is built on previous levels, and they are all 'well-founded'.
Foundation Axiom: an nonempty set has a member disjoint from it [Hart,WD]
     Full Idea: The usual statement of Foundation is that any nonempty set has a member disjoint from it. This phrasing is ordinal-free and closer to the primitives of ZFC.
     From: William D. Hart (The Evolution of Logic [2010], 3)
4. Formal Logic / F. Set Theory ST / 4. Axioms for Sets / j. Axiom of Choice IX
We can choose from finite and evident sets, but not from infinite opaque ones [Hart,WD]
     Full Idea: When a set is finite, we can prove it has a choice function (∀x x∈A → f(x)∈A), but we need an axiom when A is infinite and the members opaque. From infinite shoes we can pick a left one, but from socks we need the axiom of choice.
     From: William D. Hart (The Evolution of Logic [2010], 1)
     A reaction: The socks example in from Russell 1919:126.
With the Axiom of Choice every set can be well-ordered [Hart,WD]
     Full Idea: It follows from the Axiom of Choice that every set can be well-ordered.
     From: William D. Hart (The Evolution of Logic [2010], 1)
     A reaction: For 'well-ordered' see Idea 13460. Every set can be ordered with a least member.
4. Formal Logic / F. Set Theory ST / 4. Axioms for Sets / o. Axiom of Constructibility V = L
If we accept that V=L, it seems to settle all the open questions of set theory [Hart,WD]
     Full Idea: It has been said (by Burt Dreben) that the only reason set theorists do not generally buy the view that V = L is that it would put them out of business by settling their open questions.
     From: William D. Hart (The Evolution of Logic [2010], 10)
     A reaction: Hart says V=L breaks with the interative conception of sets at level ω+1, which is countable is the constructible view, but has continuum many in the cumulative (iterative) hierarch. The constructible V=L view is anti-platonist.
4. Formal Logic / F. Set Theory ST / 5. Conceptions of Set / d. Naïve logical sets
Naïve set theory has trouble with comprehension, the claim that every predicate has an extension [Hart,WD]
     Full Idea: 'Comprehension' is the assumption that every predicate has an extension. Naïve set theory is the theory whose axioms are extensionality and comprehension, and comprehension is thought to be its naivety.
     From: William D. Hart (The Evolution of Logic [2010], 1)
     A reaction: This doesn't, of course, mean that there couldn't be a more modest version of comprehension. The notorious difficulty come with the discovery of self-referring predicates which can't possibly have extensions.
4. Formal Logic / F. Set Theory ST / 5. Conceptions of Set / e. Iterative sets
The iterative conception may not be necessary, and may have fixed points or infinitely descending chains [Hart,WD]
     Full Idea: That the iterative sets suffice for most of ZFC does not show they are necessary, nor is it evident that the set of operations has no fixed points (as 0 is a fixed point for square-of), and no infinitely descending chains (like negative integers).
     From: William D. Hart (The Evolution of Logic [2010], 3)
     A reaction: People don't seem to worry that they aren't 'necessary', and further measures are possible to block infinitely descending chains.
4. Formal Logic / F. Set Theory ST / 6. Ordering in Sets
A 'partial ordering' is irreflexive and transitive; the sets are ordered, but not the subsets [Hart,WD]
     Full Idea: We say that a binary relation R 'partially orders' a field A just in case R is irreflexive (so that nothing bears R to itself) and transitive. When the set is {a,b}, its subsets {a} and {b} are incomparable in a partial ordering.
     From: William D. Hart (The Evolution of Logic [2010], 1)
A partial ordering becomes 'total' if any two members of its field are comparable [Hart,WD]
     Full Idea: A partial ordering is a 'total ordering' just in case any two members of its field are comparable, that is, either a is R to b, or b is R to a, or a is b.
     From: William D. Hart (The Evolution of Logic [2010], 1)
     A reaction: See Idea 13457 for 'partial ordering'. The three conditions are known as the 'trichotomy' condition.
'Well-ordering' must have a least member, so it does the natural numbers but not the integers [Hart,WD]
     Full Idea: A total order 'well-orders' its field just in case any nonempty subset B of its field has an R-least member, that is, there is a b in B such that for any a in B different from b, b bears R to a. So less-than well-orders natural numbers, but not integers.
     From: William D. Hart (The Evolution of Logic [2010], 1)
     A reaction: The natural numbers have a starting point, but the integers are infinite in both directions. In plain English, an order is 'well-ordered' if there is a starting point.
Von Neumann defines α<β as α∈β [Hart,WD]
     Full Idea: One of the glories of Von Neumann's theory of numbers is to define α < β to mean that α ∈ β.
     From: William D. Hart (The Evolution of Logic [2010], 3)
4. Formal Logic / F. Set Theory ST / 8. Critique of Set Theory
Maybe sets should be rethought in terms of the even more basic categories [Hart,WD]
     Full Idea: Some have claimed that sets should be rethought in terms of still more basic things, categories.
     From: William D. Hart (The Evolution of Logic [2010], 2)
     A reaction: [He cites F.William Lawvere 1966] It appears to the the context of foundations for mathematics that he has in mind.
5. Theory of Logic / G. Quantification / 3. Objectual Quantification
The universal quantifier can't really mean 'all', because there is no universal set [Hart,WD]
     Full Idea: All the main set theories deny that there is a set of which everything is a member. No interpretation has a domain with everything in it. So the universal quantifier never gets to mean everything all at once; 'all' does not mean all.
     From: William D. Hart (The Evolution of Logic [2010], 4)
     A reaction: Could you have an 'uncompleted' universal set, in the spirit of uncompleted infinities? In ordinary English we can talk about 'absolutely everything' - we just can't define a set of everything. Must we 'define' our domain?
5. Theory of Logic / J. Model Theory in Logic / 1. Logical Models
Modern model theory begins with the proof of Los's Conjecture in 1962 [Hart,WD]
     Full Idea: The beginning of modern model theory was when Morley proved Los's Conjecture in 1962 - that a complete theory in a countable language categorical in one uncountable cardinal is categorical in all.
     From: William D. Hart (The Evolution of Logic [2010], 9)
Model theory studies how set theory can model sets of sentences [Hart,WD]
     Full Idea: Modern model theory investigates which set theoretic structures are models for which collections of sentences.
     From: William D. Hart (The Evolution of Logic [2010], 4)
     A reaction: So first you must choose your set theory (see Idea 13497). Then you presumably look at how to formalise sentences, and then look at the really tricky ones, many of which will involve various degrees of infinity.
Model theory is mostly confined to first-order theories [Hart,WD]
     Full Idea: There is no developed methematics of models for second-order theories, so for the most part, model theory is about models for first-order theories.
     From: William D. Hart (The Evolution of Logic [2010], 9)
Models are ways the world might be from a first-order point of view [Hart,WD]
     Full Idea: Models are ways the world might be from a first-order point of view.
     From: William D. Hart (The Evolution of Logic [2010], 9)
5. Theory of Logic / K. Features of Logics / 6. Compactness
First-order logic is 'compact': consequences of a set are consequences of a finite subset [Hart,WD]
     Full Idea: First-order logic is 'compact', which means that any logical consequence of a set (finite or infinite) of first-order sentences is a logical consequence of a finite subset of those sentences.
     From: William D. Hart (The Evolution of Logic [2010], 3)
5. Theory of Logic / L. Paradox / 4. Paradoxes in Logic / c. Berry's paradox
Berry's Paradox: we succeed in referring to a number, with a term which says we can't do that [Hart,WD]
     Full Idea: Berry's Paradox: by the least number principle 'the least number denoted by no description of fewer than 79 letters' exists, but we just referred to it using a description of 77 letters.
     From: William D. Hart (The Evolution of Logic [2010], 3)
     A reaction: I struggle with this. If I refer to 'an object to which no human being could possibly refer', have I just referred to something? Graham Priest likes this sort of idea.
5. Theory of Logic / L. Paradox / 5. Paradoxes in Set Theory / c. Burali-Forti's paradox
The Burali-Forti paradox is a crisis for Cantor's ordinals [Hart,WD]
     Full Idea: The Burali-Forti Paradox was a crisis for Cantor's theory of ordinal numbers.
     From: William D. Hart (The Evolution of Logic [2010], 3)
5. Theory of Logic / L. Paradox / 6. Paradoxes in Language / a. The Liar paradox
The machinery used to solve the Liar can be rejigged to produce a new Liar [Hart,WD]
     Full Idea: In effect, the machinery introduced to solve the liar can always be rejigged to yield another version the liar.
     From: William D. Hart (The Evolution of Logic [2010], 4)
     A reaction: [He cites Hans Herzberger 1980-81] The machinery is Tarski's device of only talking about sentences of a language by using a 'metalanguage'.
6. Mathematics / A. Nature of Mathematics / 3. Nature of Numbers / e. Ordinal numbers
The less-than relation < well-orders, and partially orders, and totally orders the ordinal numbers [Hart,WD]
     Full Idea: We can show (using the axiom of choice) that the less-than relation, <, well-orders the ordinals, ...and that it partially orders the ordinals, ...and that it totally orders the ordinals.
     From: William D. Hart (The Evolution of Logic [2010], 1)
The axiom of infinity with separation gives a least limit ordinal ω [Hart,WD]
     Full Idea: The axiom of infinity with separation yields a least limit ordinal, which is called ω.
     From: William D. Hart (The Evolution of Logic [2010], 3)
There are at least as many infinite cardinals as transfinite ordinals (because they will map) [Hart,WD]
     Full Idea: Since we can map the transfinite ordinals one-one into the infinite cardinals, there are at least as many infinite cardinals as transfinite ordinals.
     From: William D. Hart (The Evolution of Logic [2010], 1)
Von Neumann's ordinals generalise into the transfinite better, because Zermelo's ω is a singleton [Hart,WD]
     Full Idea: It is easier to generalize von Neumann's finite ordinals into the transfinite. All Zermelo's nonzero finite ordinals are singletons, but if ω were a singleton it is hard to see how if could fail to be the successor of its member and so not a limit.
     From: William D. Hart (The Evolution of Logic [2010], 3)
6. Mathematics / A. Nature of Mathematics / 3. Nature of Numbers / g. Real numbers
19th century arithmetization of analysis isolated the real numbers from geometry [Hart,WD]
     Full Idea: The real numbers were not isolated from geometry until the arithmetization of analysis during the nineteenth century.
     From: William D. Hart (The Evolution of Logic [2010], 1)
6. Mathematics / A. Nature of Mathematics / 5. The Infinite / a. The Infinite
We can establish truths about infinite numbers by means of induction [Hart,WD]
     Full Idea: Mathematical induction is a way to establish truths about the infinity of natural numbers by a finite proof.
     From: William D. Hart (The Evolution of Logic [2010], 5)
     A reaction: If there are truths about infinities, it is very tempting to infer that the infinities must therefore 'exist'. A nice, and large, question in philosophy is whether there can be truths without corresponding implications of existence.
6. Mathematics / B. Foundations for Mathematics / 3. Axioms for Geometry
Euclid has a unique parallel, spherical geometry has none, and saddle geometry has several [Hart,WD]
     Full Idea: There is a familiar comparison between Euclid (unique parallel) and 'spherical' geometry (no parallel) and 'saddle' geometry (several parallels).
     From: William D. Hart (The Evolution of Logic [2010], 2)
6. Mathematics / C. Sources of Mathematics / 6. Logicism / d. Logicism critique
Mathematics makes existence claims, but philosophers usually say those are never analytic [Hart,WD]
     Full Idea: The thesis that no existence proposition is analytic is one of the few constants in philosophical consciences, but there are many existence claims in mathematics, such as the infinity of primes, five regular solids, and certain undecidable propositions.
     From: William D. Hart (The Evolution of Logic [2010], 2)
7. Existence / A. Nature of Existence / 3. Being / a. Nature of Being
Absolute thought remains in another world from being [Feuerbach]
     Full Idea: Absolute thought never extricates itself from itself to become being. Being remains in another world. …If being is to be added to an object of thought, so must something distinct from thought be added to thought itself.
     From: Ludwig Feuerbach (Principles of Philosophy of the Future [1843], §24/5)
     A reaction: This sounds a bit like a child wishing for the moon. Is he saying he doesn't just want to think about reality - he wants his mental states to BE external reality? The distinction between a thought and its content or intentionality would help here.
Being is what is undetermined, and hence indistinguishable [Feuerbach]
     Full Idea: Being in the sense in which it is an object of speculative thought is that which is purely and simply unmediated, that is, undetermined; in other words, there is nothing to distinguish and nothing to think of in being.
     From: Ludwig Feuerbach (Principles of Philosophy of the Future [1843], 26)
     A reaction: This sounds remarkably like the idea of 'prime matter' used in scholastic Aristotelian philosophy. Matter existing without form is somehow ungraspable, but presented from Hegel onwards as the ultimate mystery.
7. Existence / A. Nature of Existence / 3. Being / f. Primary being
Being posits essence, and my essence is my being [Feuerbach]
     Full Idea: Being is the positing of essence. That which is my essence is my being. The fish exists in water; you cannot, however, separate its essence from this being.
     From: Ludwig Feuerbach (Principles of Philosophy of the Future [1843], §27)
     A reaction: This throws a different light on later (e.g. Heidegger) discussions of 'being', which may map onto Aristotelian discussions of essences.
7. Existence / A. Nature of Existence / 3. Being / g. Particular being
Particularity belongs to being, whereas generality belongs to thought [Feuerbach]
     Full Idea: Particularity and individuality belong to being, whereas generality belongs to thought.
     From: Ludwig Feuerbach (Principles of Philosophy of the Future [1843], §29)
     A reaction: This agrees with Russell's view that every sentence (and proposition) must contain a universal (i.e a generality). The very notion of thinking 'about' a horse seems to require a move to the universal concept of a horse.
7. Existence / A. Nature of Existence / 3. Being / h. Dasein (being human)
The only true being is of the senses, perception, feeling and love [Feuerbach]
     Full Idea: Being as an object of being - and only this being is being and deserves the name of being - is the being of the senses, perception, feeling, and love. …Only passion is the hallmark of existence.
     From: Ludwig Feuerbach (Principles of Philosophy of the Future [1843], §33)
     A reaction: This remark seems to make Feuerbach a romantic and anti-Enlightenment figure. I don't see why there shouldn't be just as much 'being' in doing maths as in admiring a landscape. The mention of love links him to Empedocles (Ideas 459 + 630).
7. Existence / C. Structure of Existence / 8. Stuff / a. Pure stuff
Mass words do not have plurals, or numerical adjectives, or use 'fewer' [Hart,WD]
     Full Idea: Jespersen calls a noun a mass word when it has no plural, does not take numerical adjectives, and does not take 'fewer'.
     From: William D. Hart (The Evolution of Logic [2010], 3)
     A reaction: Jespersen was a great linguistics expert.
11. Knowledge Aims / C. Knowing Reality / 3. Idealism / b. Transcendental idealism
Consciousness is absolute reality, and everything exists through consciousness [Feuerbach]
     Full Idea: Consciousness is the absolute reality, the measure of all existence; all that exists, exists only as being for consciousness, as comprehended in consciousness; for consciousness is first and foremost being.
     From: Ludwig Feuerbach (Principles of Philosophy of the Future [1843], §17)
     A reaction: This is Feuerbach declaring himself in favour of idealism even as he was trying to rebel against it, and move towards a more sensuous and human view of the world. I just see idealists as confusing ontology and epistemology.
11. Knowledge Aims / C. Knowing Reality / 4. Solipsism
Ideas arise through communication, and reason is reached through community [Feuerbach]
     Full Idea: Only through communication and conversation between man and man do ideas arise; not alone, but only with others, does one reach notions and reason in general.
     From: Ludwig Feuerbach (Principles of Philosophy of the Future [1843], §41)
     A reaction: This is a strikingly modern view of the solipsism problem, and is close in spirit to Wittgenstein's Private Language Argument (Ideas 4143 +4158). Feuerbach is interested in universals rather than rules. I prefer Feuerbach.
12. Knowledge Sources / A. A Priori Knowledge / 2. Self-Evidence
Fregean self-evidence is an intrinsic property of basic truths, rules and definitions [Hart,WD]
     Full Idea: The conception of Frege is that self-evidence is an intrinsic property of the basic truths, rules, and thoughts expressed by definitions.
     From: William D. Hart (The Evolution of Logic [2010], p.350)
     A reaction: The problem is always that what appears to be self-evident may turn out to be wrong. Presumably the effort of arriving at a definition ought to clarify and support the self-evident ingredient.
12. Knowledge Sources / A. A Priori Knowledge / 11. Denying the A Priori
The failure of key assumptions in geometry, mereology and set theory throw doubt on the a priori [Hart,WD]
     Full Idea: In the case of the parallels postulate, Euclid's fifth axiom (the whole is greater than the part), and comprehension, saying was believing for a while, but what was said was false. This should make a shrewd philosopher sceptical about a priori knowledge.
     From: William D. Hart (The Evolution of Logic [2010], 2)
     A reaction: Euclid's fifth is challenged by infinite numbers, and comprehension is challenged by Russell's paradox. I can't see a defender of the a priori being greatly worried about these cases. No one ever said we would be right - in doing arithmetic, for example.
12. Knowledge Sources / B. Perception / 6. Inference in Perception
In man the lowest senses of smell and taste elevate themselves to intellectual acts [Feuerbach]
     Full Idea: Even the lowest senses, smell and taste, elevate themselves in man to intellectual and scientific acts.
     From: Ludwig Feuerbach (Principles of Philosophy of the Future [1843], §53)
     A reaction: Since Darwin we have, I am glad to say, lost this need to distinguish what is 'low' or 'high', and to try to show that even our 'lowest' functions are on the 'high' side. Personally, though, I still need the low/high distinction in moral thinking.
14. Science / B. Scientific Theories / 2. Aim of Science
Science has to abstract out the subjective attributes of things, focusing on what is objective [Aho]
     Full Idea: Crucial to the scientific method is the ability to abstract out the subjective qualities that we give to things - such as beauty, meaning, purpose, and value - and focus only on the objective qualities of things, which can be measured and quantified.
     From: Kevin Aho (Existentialism: an introduction [2014], 1 'Emergence')
     A reaction: This seems to me exactly right. People who deny the primary/secondary distinction, like Hume, are usually correspondingly pessimistic about science. And Hume was wrong about that.
18. Thought / D. Concepts / 3. Ontology of Concepts / c. Fregean concepts
The Fregean concept of GREEN is a function assigning true to green things, and false to the rest [Hart,WD]
     Full Idea: A Fregean concept is a function that assigns to each object a truth value. So instead of the colour green, the concept GREEN assigns truth to each green thing, but falsity to anything else.
     From: William D. Hart (The Evolution of Logic [2010], 2)
     A reaction: This would seem to immediately hit the renate/cordate problem, if there was a world in which all and only the green things happened to be square. How could Frege then distinguish the green from the square? Compare Idea 8245.
18. Thought / E. Abstraction / 1. Abstract Thought
The new philosophy thinks of the concrete in a concrete (not a abstract) manner [Feuerbach]
     Full Idea: The new philosophy is the philosophy that thinks of the concrete not in an abstract, but in a concrete manner.
     From: Ludwig Feuerbach (Principles of Philosophy of the Future [1843], §31)
     A reaction: This leads to placing a high value on art, and on virtuous action through particulars rather than principles, and on empirical science. The only problem is that what he proposes is impossible. To think 'about' is to abstract from the particulars.
22. Metaethics / A. Ethics Foundations / 2. Source of Ethics / d. Biological ethics
Plotinus was ashamed to have a body [Feuerbach]
     Full Idea: Plotinus, according to his biographers, was ashamed to have a body.
     From: Ludwig Feuerbach (Principles of Philosophy of the Future [1843], §29)
     A reaction: When Feuerbach draws our attention to this, we see what an astonishing state it is for a human being to have got into. Modern thought is appalled by it, but it also has something heroic about it, like swimming all the time because you want to be a fish.
22. Metaethics / B. Value / 2. Values / g. Love
If you love nothing, it doesn't matter whether something exists or not [Feuerbach]
     Full Idea: To him who loves nothing it is all the same whether something does or does not exist.
     From: Ludwig Feuerbach (Principles of Philosophy of the Future [1843], §33)
     A reaction: This seems to me to be quite a good motto for the aim of education - just get them to love something, no matter what (well, almost!). Loving something, even if it is train-spotting, seems a good route to human happiness.
23. Ethics / F. Existentialism / 3. Angst
Anxiety, nausea, guilt and absurdity shake us up, revealing our freedom and limits [Aho]
     Full Idea: Some moods, such as 'anxiety' (Heidegger), 'nausea' (Sartre), 'guilt' (Kierkegaard), and 'absurdity' (Camus) are important because they have the capacity to shake us out of complacency and self-deception, disclosing our freedom and finitude.
     From: Kevin Aho (Existentialism: an introduction [2014], Pref 'What?)
     A reaction: [bit compressed] Problem: if I fail to feel such things, and deliberately induce them in myself, am I being inauthentic? Making a huge and unnatural effort to be an existentialist seems all wrong. And who wants the permanent grip of such feelings?
23. Ethics / F. Existentialism / 5. Existence-Essence
Our 'existence' is how we create ourselves, unconstrained by any prior 'essence' [Aho]
     Full Idea: 'Existence precedes essence' means there is no pre-given 'essence' that determines who and what we are. We are self-making beings.
     From: Kevin Aho (Existentialism: an introduction [2014], Pref 'What?)
     A reaction: This not a yes/no dilemma. Personally I believe (with Aristotle, and Steven Pinker) that there is a fairly comprehensive 'human nature' which we all share, and is the basis of ethics. On top of that, though, a fair bit of 'self-making' can go on.
23. Ethics / F. Existentialism / 6. Authentic Self
The self is constituted by its choices made within a social context [Aho]
     Full Idea: The [existential] self is constituted by the continuous, open-ended process of choosing and pulling together the social interpretations that we care about and that are made available by the situation we grow into.
     From: Kevin Aho (Existentialism: an introduction [2014], 4 'Self')
     A reaction: These kind of explanations always seem wrong. That the self is influenced and moulded strongly by the choices it makes sounds right. But that the choices 'constitute' the chooser sounds like a bit of a muddle.
24. Political Theory / A. Basis of a State / 1. A People / a. Human distinctiveness
Man is not a particular being, like animals, but a universal being [Feuerbach]
     Full Idea: Man is not a particular being, like the animals, but a universal being.
     From: Ludwig Feuerbach (Principles of Philosophy of the Future [1843], §53)
     A reaction: This sounds a bit extravagent. The capacity of man to use universals in thought seems crucial to Feuerbach (though he doesn't directly address the problem). 'We are particulars with access to universals' sounds better.
The essence of man is in community, but with distinct individuals [Feuerbach]
     Full Idea: The essence of man is contained only in the community and unity of man and man; it is a unity, however, which rests only on the reality of the distinction between I and thou.
     From: Ludwig Feuerbach (Principles of Philosophy of the Future [1843], §59)
     A reaction: In English provincial suburbs (where I live) it is astonishing how little interest in and need for their neighbours people seem to have. People seem to survive without community. Most of us, though, think full human happiness needs community.
24. Political Theory / B. Nature of a State / 2. State Legitimacy / c. Social contract
Social contracts and markets have made society seem disconnected and artificial [Aho]
     Full Idea: Modern society has come to be viewed as something artificial, an aggregate of disconnected individuals that is held together by instrumental social contracts and monetary exchanges.
     From: Kevin Aho (Existentialism: an introduction [2014], 1 'Emergence')
     A reaction: This is all long of you, Thomas Hobbes! Aho is explaining the rebellion of existentialists against this - though existentialism strikes me as another variant of liberal individualism.
28. God / B. Proving God / 2. Proofs of Reason / a. Ontological Proof
God's existence cannot be separated from essence and concept, which can only be thought as existing [Feuerbach]
     Full Idea: God is the being in which existence cannot be separated from essence and concept and which cannot be thought except as existing.
     From: Ludwig Feuerbach (Principles of Philosophy of the Future [1843], §18)
     A reaction: This shows how faith in God endured through the Idealist movement by means of the Ontological Argument, despite the criticisms of Hume and Kant. To me this now appears as an odd abberation in the history of human thought.
28. God / C. Attitudes to God / 4. God Reflects Humanity
If God is only an object for man, then only the essence of man is revealed in God [Feuerbach]
     Full Idea: If God is only an object of man, what is revealed to us in his essence? Nothing but the essence of man.
     From: Ludwig Feuerbach (Principles of Philosophy of the Future [1843], §07)
     A reaction: It is important to distinguish here between what we could know about God, and what we think God might actually be like. We may well only be able to read the essence of man into God, but we might speculate that God is more than that.
God is what man would like to be [Feuerbach]
     Full Idea: God is what man would like to be.
     From: Ludwig Feuerbach (Principles of Philosophy of the Future [1843], §29)
     A reaction: It is hard to see how even the most devout person could deny the truth of this. Perhaps the essential hallmark of humanity is a desire to be different from the way we are.
God is for us a mere empty idea, which we fill with our own ego and essence [Feuerbach]
     Full Idea: God exists, but he is for us a tabula rasa, an empty being, a mere idea; God, as we conceive and think of him, is our ego, our mind, and our essence.
     From: Ludwig Feuerbach (Principles of Philosophy of the Future [1843], §17)
     A reaction: He accepted God's existence because of the Ontological Argument. This is a little stronger than Hume's view (Idea 2185), because Hume seems to be talking about imagining God, but Feuerbach says this is our understanding of God.
29. Religion / B. Monotheistic Religion / 4. Christianity / a. Christianity
Catholicism concerns God in himself, Protestantism what God is for man [Feuerbach]
     Full Idea: Protestantism is no longer concerned, as Catholicism is, about what God is in himself, but about what he is for man.
     From: Ludwig Feuerbach (Principles of Philosophy of the Future [1843], §02)
     A reaction: It is certainly true that the major religions in their origins seem to be almost exclusively concerned with God alone, and have little interest in human life (or morality).
Protestantism brought the modern emphasis on inner states of the soul [Aho]
     Full Idea: An important development in the formation of the modern worldview was the emergence of Protestantism, that reconfigured the self by privileging the inner states of the soul. Salvation concerns inner feelings, thoughts and desires, which can be genuine.
     From: Kevin Aho (Existentialism: an introduction [2014], 1 'Emergence')
     A reaction: [bit compressed] He is preparing the historical background for the existentialist concept of authenticity. We can link this Protestant idea with Descartes's Cogito, which grounds knowledge in the inner self.
29. Religion / C. Spiritual Disciplines / 3. Buddhism
Four Noble Truths: life is suffering, caused by attachment, it is avoidable, there is a path [Aho]
     Full Idea: The teachings of the Buddha are summarised in 'four noble truths': 1) life means suffering, 2) the origin of suffering is attachment, 3) the end of suffering is attainable, and 4) the path to the end of suffering.
     From: Kevin Aho (Existentialism: an introduction [2014], 9 'dukkha')
     A reaction: 1) and 2) summarise everything I dislike about most eastern philosophy. In the modern world life does not have to be suffering. To break off attachments in order to avoid suffering is a hideous injunction.
29. Religion / D. Religious Issues / 1. Religious Commitment / a. Religious Belief
Absolute idealism is the realized divine mind of Leibnizian theism [Feuerbach]
     Full Idea: Absolute idealism is nothing but the realized divine mind of Leibnizian theism.
     From: Ludwig Feuerbach (Principles of Philosophy of the Future [1843], §10)
     A reaction: In general it seems an accurate commentary that during the eighteenth century philosophers on the continent were designing a religion without God. Kantian duty tries to replace the authority of God with pure reason.