21 ideas
| 23657 | The existence of tensed verbs shows that not all truths are necessary truths [Reid] |
| Full Idea: If all truths were necessary truths, there would be no occasion for different tenses in the verbs by which they are expressed. | |
| From: Thomas Reid (Essays on Intellectual Powers 6: Judgement [1785], 5) | |
| A reaction: This really is like modern linguistic analysis. Of course the tensed verbs might only indicate times when the universal necessities have been noticed by speakers. …But then the noticing would be contingent! |
| 23655 | An ad hominem argument is good, if it is shown that the man's principles are inconsistent [Reid] |
| Full Idea: It is a good argument ad hominem, if it can be shewn that a first principle which a man rejects, stands upon the same footing with others which he admits, …for he must then be guilty of an inconsistency. | |
| From: Thomas Reid (Essays on Intellectual Powers 6: Judgement [1785], 4) | |
| A reaction: Good point. You can't divorce 'pure' reason from the reasoners, because the inconsistency of two propositions only matters when they are both asserted together. …But attacking the ideas isn't quite the same as attacking the person. |
| 10282 | Logic is the study of sound argument, or of certain artificial languages (or applying the latter to the former) [Hodges,W] |
| Full Idea: A logic is a collection of closely related artificial languages, and its older meaning is the study of the rules of sound argument. The languages can be used as a framework for studying rules of argument. | |
| From: Wilfrid Hodges (First-Order Logic [2001], 1.1) | |
| A reaction: [Hodges then says he will stick to the languages] The suspicion is that one might confine the subject to the artificial languages simply because it is easier, and avoids the tricky philosophical questions. That approximates to computer programming. |
| 10283 | A formula needs an 'interpretation' of its constants, and a 'valuation' of its variables [Hodges,W] |
| Full Idea: To have a truth-value, a first-order formula needs an 'interpretation' (I) of its constants, and a 'valuation' (ν) of its variables. Something in the world is attached to the constants; objects are attached to variables. | |
| From: Wilfrid Hodges (First-Order Logic [2001], 1.3) |
| 10284 | There are three different standard presentations of semantics [Hodges,W] |
| Full Idea: Semantic rules can be presented in 'Tarski style', where the interpretation-plus-valuation is reduced to the same question for simpler formulas, or the 'Henkin-Hintikka style' in terms of games, or the 'Barwise-Etchemendy style' for computers. | |
| From: Wilfrid Hodges (First-Order Logic [2001], 1.3) | |
| A reaction: I haven't yet got the hang of the latter two, but I note them to map the territory. |
| 10285 | I |= φ means that the formula φ is true in the interpretation I [Hodges,W] |
| Full Idea: I |= φ means that the formula φ is true in the interpretation I. | |
| From: Wilfrid Hodges (First-Order Logic [2001], 1.5) | |
| A reaction: [There should be no space between the vertical and the two horizontals!] This contrasts with |-, which means 'is proved in'. That is a syntactic or proof-theoretic symbol, whereas |= is a semantic symbol (involving truth). |
| 10288 | Down Löwenheim-Skolem: if a countable language has a consistent theory, that has a countable model [Hodges,W] |
| Full Idea: Downward Löwenheim-Skolem (the weakest form): If L is a first-order language with at most countably many formulas, and T is a consistent theory in L. Then T has a model with at most countably many elements. | |
| From: Wilfrid Hodges (First-Order Logic [2001], 1.10) |
| 10289 | Up Löwenheim-Skolem: if infinite models, then arbitrarily large models [Hodges,W] |
| Full Idea: Upward Löwenheim-Skolem: every first-order theory with infinite models has arbitrarily large models. | |
| From: Wilfrid Hodges (First-Order Logic [2001], 1.10) |
| 10287 | If a first-order theory entails a sentence, there is a finite subset of the theory which entails it [Hodges,W] |
| Full Idea: Compactness Theorem: suppose T is a first-order theory, ψ is a first-order sentence, and T entails ψ. Then there is a finite subset U of T such that U entails ψ. | |
| From: Wilfrid Hodges (First-Order Logic [2001], 1.10) | |
| A reaction: If entailment is possible, it can be done finitely. |
| 10286 | A 'set' is a mathematically well-behaved class [Hodges,W] |
| Full Idea: A 'set' is a mathematically well-behaved class. | |
| From: Wilfrid Hodges (First-Order Logic [2001], 1.6) |
| 23659 | If someone denies that he is thinking when he is conscious of it, we can only laugh [Reid] |
| Full Idea: If any man could be found so frantic as to deny that he thinks, while he is conscious of it, I may wonder, I may laugh, or I may pity him, but I cannot reason the matter with him. | |
| From: Thomas Reid (Essays on Intellectual Powers 6: Judgement [1785], 5) | |
| A reaction: An example of the influence of Descartes' Cogito running through all subsequent European philosophy. There remain the usual questions about personal identity which then arise, but Reid addresses those. |
| 23662 | The existence of ideas is no more obvious than the existence of external objects [Reid] |
| Full Idea: If external objects be perceived immediately, we have the same reason to believe their existence as philosophers have to believe the existence of ideas. | |
| From: Thomas Reid (Essays on Intellectual Powers 6: Judgement [1785], 5) | |
| A reaction: He doesn't pay much attention to mirages and delusions, but in difficult conditions of perception we are confident of our experiences but doubtful about the objects they represent. |
| 23661 | We are only aware of other beings through our senses; without that, we are alone in the universe [Reid] |
| Full Idea: We can have no communication, no correspondence or society with any created being, but by means of our senses. And, until we rely on their testimony, we must consider ourselves as being alone in the universe. | |
| From: Thomas Reid (Essays on Intellectual Powers 6: Judgement [1785], 5) | |
| A reaction: I'm not aware of any thinker before this so directly addressing solipsism. Even the champion of direct and common sense realism has to recognise the intermediary of our senses when accepting other minds. |
| 23654 | In obscure matters the few must lead the many, but the many usually lead in common sense [Reid] |
| Full Idea: In matters beyond the reach of common understanding, the many are led by the few, and willingly yield to their authority. But, in matters of common sense, the few must yield to the many, when local and temporary prejudices are removed. | |
| From: Thomas Reid (Essays on Intellectual Powers 6: Judgement [1785], 4) | |
| A reaction: Wishful thinking in the 21st century, when the many routinely deny the authority of the expert few, and the expert few occasionally prove that the collective common sense of the many is delusional. I still sort of agree with Reid. |
| 23660 | The theory of ideas, popular with philosophers, means past existence has to be proved [Reid] |
| Full Idea: The theory concerning ideas, so generally received by philosophers, destroys all the authority of memory. …This theory made it necessary for them to find out arguments to prove the existence of external objects …and of things past. | |
| From: Thomas Reid (Essays on Intellectual Powers 6: Judgement [1785], 5) | |
| A reaction: Reid was a very articulate direct realist. He seems less aware than the rest of us of the problem of delusions and false memories. Our strong sense that immediate memories are reliable is certainly inexplicable. |
| 23658 | Consciousness is an indefinable and unique operation [Reid] |
| Full Idea: Consciousness is an operation of the understanding of its own kind, and cannot be logically defined. | |
| From: Thomas Reid (Essays on Intellectual Powers 6: Judgement [1785], 5) | |
| A reaction: It is interesting that has tried to define consciousness, rather than just assuming it. I note that he calls consciousness an 'operation', rather than an entity. Good. |
| 23656 | The structure of languages reveals a uniformity in basic human opinions [Reid] |
| Full Idea: What is common in the structure of languages, indicates an uniformity of opinion in those things upon which that structure is grounded. | |
| From: Thomas Reid (Essays on Intellectual Powers 6: Judgement [1785], 4) | |
| A reaction: Reid was more interested than his contemporaries in the role of language in philosophy. The first idea sounds like Chomsky. I would add to this that the uniformity of common opinion reflects uniformities in the world they are talking about. |
| 23653 | If you can't distinguish the features of a complex object, your notion of it would be a muddle [Reid] |
| Full Idea: If you perceive an object, white, round, and a foot in diameter, if you had not been able to distinguish the colour from the figure, and both from the magnitude, your senses would only give you one complex and confused notion of all these mingled together | |
| From: Thomas Reid (Essays on Intellectual Powers 6: Judgement [1785], 1) | |
| A reaction: His point is that if you reject the 'abstraction' of these qualities, you still cannot deny that distinguishing them is an essential aspect of perceiving complex things. Does this mean that animals distinguish such things? |
| 7861 | Libet says the processes initiated in the cortex can still be consciously changed [Libet, by Papineau] |
| Full Idea: Libet himself points out that the conscious decisions still have the power to 'endorse' or 'cancel', so to speak, the processes initiated by the earlier cortical activity: no action will result if the action's execution is consciously countermanded. | |
| From: report of Benjamin Libet (Unconscious Cerebral Initiative [1985]) by David Papineau - Thinking about Consciousness 1.4 | |
| A reaction: This is why Libet's findings do not imply 'epiphenomenalism'. It seems that part of a decisive action is non-conscious, undermining the all-or-nothing view of consciousness. Searle tries to smuggle in free will at this point (Idea 3817). |
| 6660 | Libet found conscious choice 0.2 secs before movement, well after unconscious 'readiness potential' [Libet, by Lowe] |
| Full Idea: Libet found that a subject's conscious choice to move was about a fifth of a second before movement, and thus later than the onset of the brain's so-called 'readiness potential', which seems to imply that unconscious processes initiates action. | |
| From: report of Benjamin Libet (Unconscious Cerebral Initiative [1985]) by E.J. Lowe - Introduction to the Philosophy of Mind Ch.9 | |
| A reaction: Of great interest to philosophers! It seems to make conscious choices epiphenomenal. The key move, I think, is to give up the idea of consciousness as being all-or-nothing. My actions are still initiated by 'me', but 'me' shades off into unconsciousness. |
| 23663 | There are axioms of taste - such as a general consensus about a beautiful face [Reid] |
| Full Idea: I think there are axioms, even in matters of taste. …I never heard of any man who thought it a beauty in a human face to want a nose, or an eye, or to have the mouth on one side. | |
| From: Thomas Reid (Essays on Intellectual Powers 6: Judgement [1785], 6) | |
| A reaction: It is hard to disagree, but the human face may be a special case, since it is so deeply embedded in the minds of even the youngest infants. More recent artists seem able to discover beauty in very unlikely places. |