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All the ideas for 'What is Logic?st1=Ian Hacking', 'The Enneads' and 'The Thought: a Logical Enquiry'

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40 ideas

2. Reason / A. Nature of Reason / 5. Objectivity
There exists a realm, beyond objects and ideas, of non-spatio-temporal thoughts [Frege, by Weiner]
2. Reason / D. Definition / 3. Types of Definition
A decent modern definition should always imply a semantics [Hacking]
3. Truth / A. Truth Problems / 2. Defining Truth
The word 'true' seems to be unique and indefinable [Frege]
3. Truth / C. Correspondence Truth / 3. Correspondence Truth critique
There cannot be complete correspondence, because ideas and reality are quite different [Frege]
3. Truth / H. Deflationary Truth / 1. Redundant Truth
The property of truth in 'It is true that I smell violets' adds nothing to 'I smell violets' [Frege]
4. Formal Logic / B. Propositional Logic PL / 2. Tools of Propositional Logic / d. Basic theorems of PL
'Thinning' ('dilution') is the key difference between deduction (which allows it) and induction [Hacking]
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]
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]
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 / J. Model Theory in Logic / 3. Löwenheim-Skolem Theorems
If it is a logic, the Löwenheim-Skolem theorem holds for it [Hacking]
7. Existence / A. Nature of Existence / 2. Types of Existence
Thoughts in the 'third realm' cannot be sensed, and do not need an owner to exist [Frege]
7. Existence / A. Nature of Existence / 3. Being / f. Primary being
Being is the product of pure intellect [Plotinus]
The One does not exist, but is the source of all existence [Plotinus]
The One is a principle which transcends Being [Plotinus]
7. Existence / A. Nature of Existence / 3. Being / g. Particular being
Number determines individual being [Plotinus]
7. Existence / D. Theories of Reality / 8. Facts / c. Facts and truths
A fact is a thought that is true [Frege]
9. Objects / A. Existence of Objects / 3. Objects in Thought
Late Frege saw his non-actual objective objects as exclusively thoughts and senses [Frege, by Dummett]
15. Nature of Minds / A. Nature of Mind / 5. Unity of Mind
If soul was like body, its parts would be separate, without communication [Plotinus]
15. Nature of Minds / B. Features of Minds / 2. Unconscious Mind
The movement of Soul is continuous, but we are only aware of the parts of it that are sensed [Plotinus]
16. Persons / D. Continuity of the Self / 2. Mental Continuity / b. Self as mental continuity
A person is the whole of their soul [Plotinus]
17. Mind and Body / A. Mind-Body Dualism / 1. Dualism
Our soul has the same ideal nature as the oldest god, and is honourable above the body [Plotinus]
The soul is outside of all of space, and has no connection to the bodily order [Plotinus]
18. Thought / A. Modes of Thought / 1. Thought
We grasp thoughts (thinking), decide they are true (judgement), and manifest the judgement (assertion) [Frege]
Thoughts have their own realm of reality - 'sense' (as opposed to the realm of 'reference') [Frege, by Dummett]
A thought is distinguished from other things by a capacity to be true or false [Frege, by Dummett]
18. Thought / A. Modes of Thought / 9. Indexical Thought
Thoughts about myself are understood one way to me, and another when communicated [Frege]
19. Language / D. Propositions / 2. Abstract Propositions / a. Propositions as sense
A 'thought' is something for which the question of truth can arise; thoughts are senses of sentences [Frege]
19. Language / D. Propositions / 5. Unity of Propositions
A sentence is only a thought if it is complete, and has a time-specification [Frege]
22. Metaethics / A. Ethics Foundations / 2. Source of Ethics / b. Rational ethics
The Soul reasons about the Right, so there must be some permanent Right about which it reasons [Plotinus]
22. Metaethics / C. The Good / 2. Happiness / a. Nature of happiness
Ecstasy is for the neo-Platonist the highest psychological state of man [Plotinus, by Feuerbach]
26. Natural Theory / A. Speculations on Nature / 6. Early Matter Theories / e. The One
How can multiple existence arise from the unified One? [Plotinus]
Soul is the logos of Nous, just as Nous is the logos of the One [Plotinus]
Because the One is immobile, it must create by radiation, light the sun producing light [Plotinus]
28. God / B. Proving God / 3. Proofs of Evidence / b. Teleological Proof
Soul is author of all of life, and of the stars, and it gives them law and movement [Plotinus]
29. Religion / D. Religious Issues / 2. Immortality / b. Soul
Even the soul is secondary to the Intellectual-Principle [Nous], of which soul is an utterance [Plotinus]