30 ideas
| 23269 | Philosophy must start from clearly observed facts [Galen] |
| Full Idea: True philosophers concern themselves first and foremost to take clearly observed facts as their point of departure. | |
| From: Galen (The soul's dependence on the body [c.170], Kiv.11.817) | |
| A reaction: I love this one, especially the desire that the facts be 'clearly observed'. That, thank goodness, eliminates quantum mechanics. If you don't love history and the physical sciences, you are not a philosopher. Oh, and reliable gossip. |
| 23248 | Early empiricists said reason was just a useless concept introduced by philosophers [Galen, by Frede,M] |
| Full Idea: The so-called Empiricists in Hellenistic times [as cited by Galen] denied the existence of reason, treating it as a useless theoretical postulate introduced by some philosophers | |
| From: report of Galen (An Outline of Empiricism [c.170], 87.4-9.28ff) by Michael Frede - Intro to 'Rationality in Greek Thought' p.3 | |
| A reaction: I think 'be sensible' is understood by everyone, but 'use your reason' is far from obvious. The main role of reason seems to be as an identifier for human exceptionalism. Animals obviously make good judgements. Frede thinks the empiricists were right. |
| 19115 | You can 'rebut' an argument's conclusion, or 'undercut' its premises [Antonelli] |
| Full Idea: A 'rebut' of an argument establishes that its conclusion is not the case. An 'undercut' of the argument shows that the premises do not support that conclusion. | |
| From: G. Aldo Antonelli (Non-Monotonic Logic [2014], 3.2) |
| 19119 | We infer that other objects are like some exceptional object, if they share some of its properties [Antonelli] |
| Full Idea: The exceptional status of an object with respect to some default is more likely to spread to other objects if they share properties with that object that may play a role in explaining the exceptional status. | |
| From: G. Aldo Antonelli (Non-Monotonic Logic [2014], 4) | |
| A reaction: This is an example of the sort of rational behaviour we exhibit, and which a 'real life' logic would somehow need to capture. I would suggest the essentialist logic designed by Kit Fine as a first port of call. |
| 19111 | Reasoning may be defeated by new premises, or by finding out more about the given ones [Antonelli] |
| Full Idea: Most defeasible reasoning is externally dynamic, affected by the addition of further premises. But there is also an internal (or 'diachronic') dynamic, when further analysis reveals more about the given premises. | |
| From: G. Aldo Antonelli (Non-Monotonic Logic [2014], 1) |
| 19113 | Weakest Link Principle: prefer the argument whose weakest link is the stronger [Antonelli] |
| Full Idea: In the Weakest Link Principle, an argument is preferred to another conflicting argument if its weakest defeasible link is stronger than the weakest defeasible link in the conflicting argument. | |
| From: G. Aldo Antonelli (Non-Monotonic Logic [2014], 2.1) | |
| A reaction: [He cites John Pollock 1991] This sounds like the elementary principle applied when choosing a rope by which to hang a large weight above your head. It gets non-monotonic logic off the ground - if you know how to evaluate 'weakest'. |
| 19114 | Should we accept Floating Conclusions, derived from two arguments in conflict? [Antonelli] |
| Full Idea: There is much discussion of whether Floating Conclusions should be derived, given that they were derived from two arguments which conflict with one another. | |
| From: G. Aldo Antonelli (Non-Monotonic Logic [2014], 2.3) |
| 19116 | Non-monotonic core: Reflexivity, Cut, Cautious Monotonicity, Left Logical Equivalence, Right Weakening [Antonelli] |
| Full Idea: Conservative core of non-monotonic logic:Reflexivity (p proves p), Cut (if p proves q, it proves their joint implications), Cautious Monotonicity, Left Logical Equivalence (equivalences have same consequences), Right Weakening (non-m preserves classical). | |
| From: G. Aldo Antonelli (Non-Monotonic Logic [2014], 3.5.1) | |
| A reaction: [Highly compressed, and without symbols] |
| 19117 | We can rank a formula by the level of surprise if it were to hold [Antonelli] |
| Full Idea: We can think of an 'ordinal ranking function' κ([φ)] as the level of surprise we would face were φ to hold, up to maximal surprise. | |
| From: G. Aldo Antonelli (Non-Monotonic Logic [2014], 3.5.2) | |
| A reaction: This suggests that Bayes's Theorem might be relevant to non-monotonic logic. This suggests that registering surprise would need to be an important feature of robot behaviour. |
| 19118 | People don't actually use classical logic, but may actually use non-monotonic logic [Antonelli] |
| Full Idea: Test subjects seem to perform very poorly in various reasoning tests (Wason Selection, Suppression Task), suggesting logic has a subordinate role, but this may be using classical logic, where non-monotonic logics would be more appropriate. | |
| From: G. Aldo Antonelli (Non-Monotonic Logic [2014], 4) | |
| A reaction: Fred Sommers presents his Term Logic (based on Aristotle) as closer to how people actually reason. It is certainly crazy to infer that most people's everyday reasoning is irrational. Induction is highly rational; it's just not deductive. |
| 18755 | Validity is explained as truth in all models, because that relies on the logical terms [McGee] |
| Full Idea: A model of a language assigns values to non-logical terms. If a sentence is true in every model, its truth doesn't depend on those non-logical terms. Hence the validity of an argument comes from its logical form. Thus models explain logical validity. | |
| From: Vann McGee (Logical Consequence [2014], 4) | |
| A reaction: [compressed] Thus you get a rigorous account of logical validity by only allowing the rigorous input of model theory. This is the modern strategy of analytic philosophy. But is 'it's red so it's coloured' logically valid? |
| 18751 | Natural language includes connectives like 'because' which are not truth-functional [McGee] |
| Full Idea: Natural language includes connectives that are not truth-functional. In order for 'p because q' to be true, both p and q have to be true, but knowing the simpler sentences are true doesn't determine whether the larger sentence is true. | |
| From: Vann McGee (Logical Consequence [2014], 2) |
| 18761 | Second-order variables need to range over more than collections of first-order objects [McGee] |
| Full Idea: To get any advantage from moving to second-order logic, we need to assign to second-order variables a role different from merely ranging over collections made up of things the first-order variables range over. | |
| From: Vann McGee (Logical Consequence [2014], 7) | |
| A reaction: Thus it is exciting if they range over genuine properties, but not so exciting if you merely characterise those properties as sets of first-order objects. This idea leads into a discussion of plural quantification. |
| 18753 | An ontologically secure semantics for predicate calculus relies on sets [McGee] |
| Full Idea: We can get a less ontologically perilous presentation of the semantics of the predicate calculus by using sets instead of concepts. | |
| From: Vann McGee (Logical Consequence [2014], 4) | |
| A reaction: The perilous versions rely on Fregean concepts, and notably Russell's 'concept that does not fall under itself'. The sets, of course, have to be ontologically secure, and so will involve the iterative conception, rather than naive set theory. |
| 18754 | Logically valid sentences are analytic truths which are just true because of their logical words [McGee] |
| Full Idea: Logically valid sentences are a species of analytic sentence, being true not just in virtue of the meanings of their words, but true in virtue of the meanings of their logical words. | |
| From: Vann McGee (Logical Consequence [2014], 4) | |
| A reaction: A helpful link between logical truths and analytic truths, which had not struck me before. |
| 18757 | Soundness theorems are uninformative, because they rely on soundness in their proofs [McGee] |
| Full Idea: Soundness theorems are seldom very informative, since typically we use informally, in proving the theorem, the very same rules whose soundness we are attempting to establish. | |
| From: Vann McGee (Logical Consequence [2014], 5) | |
| A reaction: [He cites Quine 1935] |
| 19110 | In classical logic the relation |= has Monotony built into its definition [Antonelli] |
| Full Idea: In classical logic, Monotony follows immediately from the nature of the relation |=, for Γ |= φ holds precisely when φ is true on every interpretation on which all sentences in Γ are true. | |
| From: G. Aldo Antonelli (Non-Monotonic Logic [2014], 1) | |
| A reaction: That is, semantic consequence (|=) is defined in terms of a sentence (φ) always being true if some other bunch of sentences (Γ) are true. Hence the addition of further sentences to Γ will make no difference - which is Monotony. |
| 19112 | Cautious Monotony ignores proved additions; Rational Monotony fails if the addition's negation is proved [Antonelli] |
| Full Idea: Basic Monotony: something stays proved if further premises are added. Cautious Monotony: the addition of something which has been proved makes no difference. Rational Monotony: it stays proved as long as the addition's negation hasn't been proved. | |
| From: G. Aldo Antonelli (Non-Monotonic Logic [2014], 1) | |
| A reaction: [A compressed and non-symbolic summary] |
| 18760 | The culmination of Euclidean geometry was axioms that made all models isomorphic [McGee] |
| Full Idea: One of the culminating achievements of Euclidean geometry was categorical axiomatisations, that describe the geometric structure so completely that any two models of the axioms are isomorphic. The axioms are second-order. | |
| From: Vann McGee (Logical Consequence [2014], 7) | |
| A reaction: [He cites Veblen 1904 and Hilbert 1903] For most mathematicians, categorical axiomatisation is the best you can ever dream of (rather than a single true axiomatisation). |
| 23266 | The spirit in the soul wants freedom, power and honour [Galen] |
| Full Idea: The spirited part of the soul is desiderative of freedom, victory, power, authority, reputation, and honour. | |
| From: Galen (The soul's dependence on the body [c.170], Kiv.2.772) | |
| A reaction: This is the concept of 'thumos' [spirit], taken straight from Plato's tripartite account of the soul, in 'Republic'. Note that it includes a desire for freedom (in an age of slavery). |
| 6003 | Galen showed by experiment that the brain controls the body [Galen, by Hankinson] |
| Full Idea: Galen established by experiments in neural anatomy that the brain really is, contra the Stoics and Aristotelians, the body's control centre. | |
| From: report of Galen (On Hippocrates and Plato [c.170]) by R.J. Hankinson - Galen (damaged) | |
| A reaction: And about time too. This is one of the most significant events in the development of human understanding. No one has been able to go back to the old view, even Descartes, no matter how much they may long to do so. |
| 23219 | Stopping the heart doesn't terminate activity; pressing the brain does that [Galen, by Cobb] |
| Full Idea: Even when an animals heart was stopped [by hand] it continued its muted whimpers, …but when the brain was pressed the animal stopped making a noise and became unconscious. | |
| From: report of Galen (The soul's dependence on the body [c.170]) by Matthew Cobb - The Idea of the Brain 1 | |
| A reaction: It's not that the ancients didn't do science. It's that ancient people paid no attention to what their scientists discovered. |
| 21799 | We just use the word 'faculty' when we don't know the psychological cause [Galen] |
| Full Idea: So long as we are ignorant of the true essence of the cause which is operating, we call it a 'faculty'. | |
| From: Galen (On the Natural Faculties [c.170], I.iv), quoted by Dominik Perler - Intro to The Faculties: a History 2 | |
| A reaction: This is probably the view of most modern neuroscientists. I want to defend the idea that we need the concept of a faculty in philosophy, even if the psychologists and neuroscientists say it is too vague for their purposes. |
| 23264 | Philosophers think faculties are in substances, and invent a faculty for every activity [Galen] |
| Full Idea: Philosophers conceive of faculties as things which inhabit 'substances' much as we inhabit houses, not realising that causes of events are conceived in relational terms. We therefore attribute as many faculties to a substance as activities. | |
| From: Galen (The soul's dependence on the body [c.170], Kiv.2.769) | |
| A reaction: This seems to demolish speculative faculties, but they were revived during the Enlightenment. I am happy to talk of 'philosophical faculties' where they are presumed to originate a type of thought, without commitment to any neuroscience. |
| 23220 | The brain contains memory and reason, and is the source of sensation and decision [Galen] |
| Full Idea: The brain is the principal organ of the psychical members. For within the brain is seated memory, reason and intellect, and from the brain is distributed the power, sensation and voluntary motion. | |
| From: Galen (The soul's dependence on the body [c.170]), quoted by Matthew Cobb - The Idea of the Brain 1 | |
| A reaction: [not sure of ref] Interesting that he assigns the whole of mind to the brain, and not just some aspect of it. He had done experiments. Understanding the role of the brain was amazingly slow. Impeded by religion, I guess. |
| 23265 | The rational part of the soul is the desire for truth, understanding and recollection [Galen] |
| Full Idea: That part of the soul which we call rational is desiderative: …it desires truth, knowledge, learning, understanding, and recollection - in short, all the good things. | |
| From: Galen (The soul's dependence on the body [c.170], Kiv.2.772) | |
| A reaction: Truth is no surprise, but recollection is. Note the separation of knowledge from understanding. This is a very good characterisation of rationality. For the Greeks it has a moral dimension, of wanting what is good. |
| 18762 | A maxim claims that if we are allowed to assert a sentence, that means it must be true [McGee] |
| Full Idea: If our linguistic conventions entitle us to assert a sentence, they thereby make it true, because of the maxim that 'truth is the norm of assertion'. | |
| From: Vann McGee (Logical Consequence [2014], 8) | |
| A reaction: You could only really deny that maxim if you had no belief at all in truth, but then you can assert anything you like (with full entitlement). Maybe you can assert anything you like as long as it doesn't upset anyone? Etc. |
| 7453 | Galen's medicine followed the mean; each illness was balanced by opposite treatment [Galen, by Hacking] |
| Full Idea: Galen ran medicine on the principle of the mean; afflictions must be treated by contraries; hot diseases deserve cold medicine and moist illnesses want drying agents. (Paracelsus rebelled, treating through similarity). | |
| From: report of Galen (On Medical Experience [c.169]) by Ian Hacking - The Emergence of Probability Ch.5 | |
| A reaction: This must be inherited from Aristotle, with the aim of virtue for the body, as Aristotle wanted virtue for the psuché. In some areas Galen is probably right, that natural balance is the aim, as in bodily temperature control. |
| 6030 | Each part of the soul has its virtue - pleasure for appetite, success for competition, and rectitude for reason [Galen] |
| Full Idea: We have by nature these three appropriate relationships, corresponding to each form of the soul's parts - to pleasure because of the appetitive part, to success because of the competitive part, and to rectitude because of the rational part. | |
| From: Galen (On Hippocrates and Plato [c.170], 5.5.8) | |
| A reaction: This is a nice combination of Plato's tripartite theory of soul (in 'Republic') and Aristotle's derivation of virtues from functions. Presumably, though, reason should master the other two, and there is nothing in Galen's idea to explain this. |
| 23268 | We execute irredeemable people, to protect ourselves, as a deterrent, and ending a bad life [Galen] |
| Full Idea: We kill the irredeemably wicked, for three reasons: that they may no longer harm us; as a deterrent to others like them; and because it is actually better from their own point of view to die, when their souls are so damaged they cannot be improved. | |
| From: Galen (The soul's dependence on the body [c.170], Kiv.11.816) | |
| A reaction: The third one sounds like a dubious rationalisation, given that the prisoner probably disagrees. Nowadays we are not so quick to judge someone as irredeemable. The first one works when they run wild, but not after their capture. |