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10 ideas
16867 | Logic not only proves things, but also reveals logical relations between them [Frege] |
Full Idea: A proof does not only serve to convince us of the truth of what is proved: it also serves to reveal logical relations between truths. Hence we find in Euclid proofs of truths that appear to stand in no need of proof because they are obvious without one. | |
From: Gottlob Frege (Logic in Mathematics [1914], p.204) | |
A reaction: This is a key idea in Frege's philosophy, and a reason why he is the founder of modern analytic philosophy, with logic placed at the centre of the subject. I take the value of proofs to be raising questions, more than giving answers. |
16862 | The closest subject to logic is mathematics, which does little apart from drawing inferences [Frege] |
Full Idea: Mathematics has closer ties with logic than does almost any other discipline; for almost the entire activity of the mathematician consists in drawing inferences. | |
From: Gottlob Frege (Logic in Mathematics [1914], p.203) | |
A reaction: The interesting question is who is in charge - the mathematician or the logician? |
16863 | Does some mathematical reasoning (such as mathematical induction) not belong to logic? [Frege] |
Full Idea: Are there perhaps modes of inference peculiar to mathematics which …do not belong to logic? Here one may point to inference by mathematical induction from n to n+1. | |
From: Gottlob Frege (Logic in Mathematics [1914], p.203) | |
A reaction: He replies that it looks as if induction can be reduced to general laws, and those can be reduced to logic. |
16865 | 'Theorems' are both proved, and used in proofs [Frege] |
Full Idea: Usually a truth is only called a 'theorem' when it has not merely been obtained by inference, but is used in turn as a premise for a number of inferences in the science. ….Proofs use non-theorems, which only occur in that proof. | |
From: Gottlob Frege (Logic in Mathematics [1914], p.204) |
16866 | Tracing inference backwards closes in on a small set of axioms and postulates [Frege] |
Full Idea: We can trace the chains of inference backwards, …and the circle of theorems closes in more and more. ..We must eventually come to an end by arriving at truths can cannot be inferred, …which are the axioms and postulates. | |
From: Gottlob Frege (Logic in Mathematics [1914], p.204) | |
A reaction: The rival (more modern) view is that that all theorems are equal in status, and axioms are selected for convenience. |
16868 | The essence of mathematics is the kernel of primitive truths on which it rests [Frege] |
Full Idea: Science must endeavour to make the circle of unprovable primitive truths as small as possible, for the whole of mathematics is contained in this kernel. The essence of mathematics has to be defined by this kernel of truths. | |
From: Gottlob Frege (Logic in Mathematics [1914], p.204-5) | |
A reaction: [compressed] I will make use of this thought, by arguing that mathematics may be 'explained' by this kernel. |
16871 | A truth can be an axiom in one system and not in another [Frege] |
Full Idea: It is possible for a truth to be an axiom in one system and not in another. | |
From: Gottlob Frege (Logic in Mathematics [1914], p.205) | |
A reaction: Frege aspired to one huge single system, so this is a begrudging concession, one which modern thinkers would probably take for granted. |
16870 | Axioms are truths which cannot be doubted, and for which no proof is needed [Frege] |
Full Idea: The axioms are theorems, but truths for which no proof can be given in our system, and no proof is needed. It follows from this that there are no false axioms, and we cannot accept a thought as an axiom if we are in doubt about its truth. | |
From: Gottlob Frege (Logic in Mathematics [1914], p.205) | |
A reaction: He struggles to be as objective as possible, but has to concede that whether we can 'doubt' the axiom is one of the criteria. |
13986 | Plato found antinomies in ideas, Kant in space and time, and Bradley in relations [Plato, by Ryle] |
Full Idea: Plato (in 'Parmenides') shows that the theory that 'Eide' are substances, and Kant that space and time are substances, and Bradley that relations are substances, all lead to aninomies. | |
From: report of Plato (Parmenides [c.364 BCE]) by Gilbert Ryle - Are there propositions? 'Objections' |
14150 | Plato's 'Parmenides' is perhaps the best collection of antinomies ever made [Russell on Plato] |
Full Idea: Plato's 'Parmenides' is perhaps the best collection of antinomies ever made. | |
From: comment on Plato (Parmenides [c.364 BCE]) by Bertrand Russell - The Principles of Mathematics §337 |