13 ideas
| 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] |
| 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). |
| 16664 | Everything that exists is either a substance or an accident [Albert of Saxony] |
| Full Idea: Everything that exists is either a substance or an accident. | |
| From: Albert of Saxony (On 'Physics' [1357], I.18), quoted by Robert Pasnau - Metaphysical Themes 1274-1671 13.2 | |
| A reaction: This seems to be the view of those who base their ontology on first-order classical logic. The more austere reading of that makes the accidents into sets of substances, so it's just substances. All the non-substance stuff cries out for recognition. |
| 16703 | God could make a successive thing so that previous parts cease to exist [Albert of Saxony] |
| Full Idea: Something can be conceived of as successive simpliciter, with respect to both its substance and its state. For example, if Socrates were continually made and made again by the First Cause, as the Seine flow, so nothing of what preexists remains. | |
| From: Albert of Saxony (On 'Physics' [1357], III.3), quoted by Robert Pasnau - Metaphysical Themes 1274-1671 18.4 | |
| A reaction: This is precisely the problem that modern stage theory faces, of knowing how to connect the stages together. |
| 16699 | Successive entities just need parts to succeed one another, without their existence [Albert of Saxony] |
| Full Idea: For existence to hold of completely successive entities it is not required that their parts exist, but that one part succeed another, as a future part succeeds a past part. | |
| From: Albert of Saxony (On 'Physics' [1357], III.3 ad 2), quoted by Robert Pasnau - Metaphysical Themes 1274-1671 18.3 | |
| A reaction: A nice move, but it doesn't quite solve it. How can non-existent things 'succeed one another'? It is worrying for metaphysics that some things have entirely different concepts of persistence from other things. |
| 3061 | Anaxarchus said that he was not even sure that he knew nothing [Anaxarchus, by Diog. Laertius] |
| Full Idea: Anaxarchus said that he was not even sure that he knew nothing. | |
| From: report of Anaxarchus (fragments/reports [c.340 BCE]) by Diogenes Laertius - Lives of Eminent Philosophers 09.10.1 |
| 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. |
| 16570 | Elements are found last in dismantling bodies, and first in generating them [Albert of Saxony] |
| Full Idea: On one possible description, an element is what is found last when bodies are taken apart, and what is found first when bodies are generated. | |
| From: Albert of Saxony (On 'Generation and Corruption' [1356], II.3), quoted by Robert Pasnau - Metaphysical Themes 1274-1671 2.1 |