Combining Texts

All the ideas for 'What is Logic?st1=Ian Hacking', 'Our Knowledge of the External World' and 'Summa totius logicae'

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41 ideas

1. Philosophy / A. Wisdom / 1. Nature of Wisdom
A sense of timelessness is essential to wisdom [Russell]
1. Philosophy / D. Nature of Philosophy / 7. Despair over Philosophy
Philosophical disputes are mostly hopeless, because philosophers don't understand each other [Russell]
1. Philosophy / E. Nature of Metaphysics / 3. Metaphysical Systems
Philosophical systems are interesting, but we now need a more objective scientific philosophy [Russell]
Hegel's confusions over 'is' show how vast systems can be built on simple errors [Russell]
Philosophers sometimes neglect truth and distort facts to attain a nice system [Russell]
1. Philosophy / E. Nature of Metaphysics / 4. Metaphysics as Science
Physicists accept particles, points and instants, while pretending they don't do metaphysics [Russell]
1. Philosophy / F. Analytic Philosophy / 6. Logical Analysis
When problems are analysed properly, they are either logical, or not philosophical at all [Russell]
2. Reason / B. Laws of Thought / 3. Non-Contradiction
From an impossibility anything follows [William of Ockham]
2. Reason / D. Definition / 3. Types of Definition
A decent modern definition should always imply a semantics [Hacking]
3. Truth / C. Correspondence Truth / 1. Correspondence Truth
A proposition is true if its subject and predicate stand for the same thing [William of Ockham]
3. Truth / G. Axiomatic Truth / 1. Axiomatic Truth
Ockham had an early axiomatic account of truth [William of Ockham, by Halbach]
4. Formal Logic / B. Propositional Logic PL / 2. Tools of Propositional Logic / d. Basic theorems of PL
Gentzen's Cut Rule (or transitivity of deduction) is 'If A |- B and B |- C, then A |- C' [Hacking]
Only Cut reduces complexity, so logic is constructive without it, and it can be dispensed with [Hacking]
'Thinning' ('dilution') is the key difference between deduction (which allows it) and induction [Hacking]
5. Theory of Logic / A. Overview of Logic / 3. Value of Logic
Logic gives the method of research in philosophy [Russell]
5. Theory of Logic / A. Overview of Logic / 4. Pure Logic
The various logics are abstractions made from terms like 'if...then' in English [Hacking]
5. Theory of Logic / A. Overview of Logic / 5. First-Order Logic
First-order logic is the strongest complete compact theory with Löwenheim-Skolem [Hacking]
A limitation of first-order logic is that it cannot handle branching quantifiers [Hacking]
5. Theory of Logic / A. Overview of Logic / 7. Second-Order Logic
Second-order completeness seems to need intensional entities and possible worlds [Hacking]
5. Theory of Logic / E. Structures of Logic / 2. Logical Connectives / a. Logical connectives
With a pure notion of truth and consequence, the meanings of connectives are fixed syntactically [Hacking]
The logical connectives are not objects, but are formal, and need a context [Russell]
5. Theory of Logic / E. Structures of Logic / 4. Variables in Logic
Perhaps variables could be dispensed with, by arrows joining places in the scope of quantifiers [Hacking]
5. Theory of Logic / G. Quantification / 1. Quantification
The word 'every' only signifies when added to a term such as 'man', referring to all men [William of Ockham]
5. Theory of Logic / J. Model Theory in Logic / 3. Löwenheim-Skolem Theorems
If it is a logic, the Löwenheim-Skolem theorem holds for it [Hacking]
5. Theory of Logic / L. Paradox / 4. Paradoxes in Logic / a. Achilles paradox
The tortoise won't win, because infinite instants don't compose an infinitely long time [Russell]
6. Mathematics / C. Sources of Mathematics / 5. Numbers as Adjectival
Just as unity is not a property of a single thing, so numbers are not properties of many things [William of Ockham]
7. Existence / A. Nature of Existence / 3. Being / g. Particular being
The words 'thing' and 'to be' assert the same idea, as a noun and as a verb [William of Ockham]
7. Existence / C. Structure of Existence / 6. Fundamentals / d. Logical atoms
Atomic facts may be inferrable from others, but never from non-atomic facts [Russell]
7. Existence / D. Theories of Reality / 8. Facts / d. Negative facts
A positive and negative fact have the same constituents; their difference is primitive [Russell]
8. Modes of Existence / A. Relations / 1. Nature of Relations
With asymmetrical relations (before/after) the reduction to properties is impossible [Russell]
8. Modes of Existence / B. Properties / 11. Properties as Sets
When we attribute a common quality to a group, we can forget the quality and just talk of the group [Russell]
8. Modes of Existence / E. Nominalism / 1. Nominalism / b. Nominalism about universals
Universals are single things, and only universal in what they signify [William of Ockham]
9. Objects / D. Essence of Objects / 6. Essence as Unifier
If essence and existence were two things, one could exist without the other, which is impossible [William of Ockham]
11. Knowledge Aims / C. Knowing Reality / 1. Perceptual Realism / c. Representative realism
Science condemns sense-data and accepts matter, but a logical construction must link them [Russell]
12. Knowledge Sources / B. Perception / 4. Sense Data / c. Unperceived sense-data
When sense-data change, there must be indistinguishable sense-data in the process [Russell]
12. Knowledge Sources / C. Rationalism / 1. Rationalism
Empirical truths are particular, so general truths need an a priori input of generality [Russell]
13. Knowledge Criteria / B. Internal Justification / 5. Coherentism / b. Pro-coherentism
Objects are treated as real when they connect with other experiences in a normal way [Russell]
13. Knowledge Criteria / D. Scepticism / 6. Scepticism Critique
Global scepticism is irrefutable, but can't replace our other beliefs, and just makes us hesitate [Russell]
15. Nature of Minds / A. Nature of Mind / 4. Other Minds / c. Knowing other minds
Other minds seem to exist, because their testimony supports realism about the world [Russell, by Grayling]
19. Language / D. Propositions / 4. Mental Propositions
Some concepts for propositions exist only in the mind, and in no language [William of Ockham]
27. Natural Reality / D. Time / 2. Passage of Time / a. Experience of time
We never experience times, but only succession of events [Russell]