34 ideas
| 17925 | Showing a disproof is impossible is not a proof, so don't eliminate double negation [Colyvan] |
| Full Idea: In intuitionist logic double negation elimination fails. After all, proving that there is no proof that there can't be a proof of S is not the same thing as having a proof of S. | |
| From: Mark Colyvan (Introduction to the Philosophy of Mathematics [2012], 1.1.3) | |
| A reaction: I do like people like Colyvan who explain things clearly. All of this difficult stuff is understandable, if only someone makes the effort to explain it properly. |
| 17926 | Rejecting double negation elimination undermines reductio proofs [Colyvan] |
| Full Idea: The intuitionist rejection of double negation elimination undermines the important reductio ad absurdum proof in classical mathematics. | |
| From: Mark Colyvan (Introduction to the Philosophy of Mathematics [2012], 1.1.3) |
| 17924 | Excluded middle says P or not-P; bivalence says P is either true or false [Colyvan] |
| Full Idea: The law of excluded middle (for every proposition P, either P or not-P) must be carefully distinguished from its semantic counterpart bivalence, that every proposition is either true or false. | |
| From: Mark Colyvan (Introduction to the Philosophy of Mathematics [2012], 1.1.3) | |
| A reaction: So excluded middle makes no reference to the actual truth or falsity of P. It merely says P excludes not-P, and vice versa. |
| 17929 | Löwenheim proved his result for a first-order sentence, and Skolem generalised it [Colyvan] |
| Full Idea: Löwenheim proved that if a first-order sentence has a model at all, it has a countable model. ...Skolem generalised this result to systems of first-order sentences. | |
| From: Mark Colyvan (Introduction to the Philosophy of Mathematics [2012], 2.1.2) |
| 17930 | Axioms are 'categorical' if all of their models are isomorphic [Colyvan] |
| Full Idea: A set of axioms is said to be 'categorical' if all models of the axioms in question are isomorphic. | |
| From: Mark Colyvan (Introduction to the Philosophy of Mathematics [2012], 2.1.2) | |
| A reaction: The best example is the Peano Axioms, which are 'true up to isomorphism'. Set theory axioms are only 'quasi-isomorphic'. |
| 17928 | Ordinal numbers represent order relations [Colyvan] |
| Full Idea: Ordinal numbers represent order relations. | |
| From: Mark Colyvan (Introduction to the Philosophy of Mathematics [2012], 1.2.3 n17) |
| 17923 | Intuitionists only accept a few safe infinities [Colyvan] |
| Full Idea: For intuitionists, all but the smallest, most well-behaved infinities are rejected. | |
| From: Mark Colyvan (Introduction to the Philosophy of Mathematics [2012], 1.1.3) | |
| A reaction: The intuitionist idea is to only accept what can be clearly constructed or proved. |
| 17941 | Infinitesimals were sometimes zero, and sometimes close to zero [Colyvan] |
| Full Idea: The problem with infinitesimals is that in some places they behaved like real numbers close to zero but in other places they behaved like zero. | |
| From: Mark Colyvan (Introduction to the Philosophy of Mathematics [2012], 7.1.2) | |
| A reaction: Colyvan gives an example, of differentiating a polynomial. |
| 17922 | Reducing real numbers to rationals suggested arithmetic as the foundation of maths [Colyvan] |
| Full Idea: Given Dedekind's reduction of real numbers to sequences of rational numbers, and other known reductions in mathematics, it was tempting to see basic arithmetic as the foundation of mathematics. | |
| From: Mark Colyvan (Introduction to the Philosophy of Mathematics [2012], 1.1.1) | |
| A reaction: The reduction is the famous Dedekind 'cut'. Nowadays theorists seem to be more abstract (Category Theory, for example) instead of reductionist. |
| 17936 | Transfinite induction moves from all cases, up to the limit ordinal [Colyvan] |
| Full Idea: Transfinite inductions are inductive proofs that include an extra step to show that if the statement holds for all cases less than some limit ordinal, the statement also holds for the limit ordinal. | |
| From: Mark Colyvan (Introduction to the Philosophy of Mathematics [2012], 5.2.1 n11) |
| 17940 | Most mathematical proofs are using set theory, but without saying so [Colyvan] |
| Full Idea: Most mathematical proofs, outside of set theory, do not explicitly state the set theory being employed. | |
| From: Mark Colyvan (Introduction to the Philosophy of Mathematics [2012], 7.1.1) |
| 17931 | Structuralism say only 'up to isomorphism' matters because that is all there is to it [Colyvan] |
| Full Idea: Structuralism is able to explain why mathematicians are typically only interested in describing the objects they study up to isomorphism - for that is all there is to describe. | |
| From: Mark Colyvan (Introduction to the Philosophy of Mathematics [2012], 3.1.2) |
| 17932 | If 'in re' structures relies on the world, does the world contain rich enough structures? [Colyvan] |
| Full Idea: In re structuralism does not posit anything other than the kinds of structures that are in fact found in the world. ...The problem is that the world may not provide rich enough structures for the mathematics. | |
| From: Mark Colyvan (Introduction to the Philosophy of Mathematics [2012], 3.1.2) | |
| A reaction: You can perceive a repeating pattern in the world, without any interest in how far the repetitions extend. |
| 17943 | Probability supports Bayesianism better as degrees of belief than as ratios of frequencies [Colyvan] |
| Full Idea: Those who see probabilities as ratios of frequencies can't use Bayes's Theorem if there is no objective prior probability. Those who accept prior probabilities tend to opt for a subjectivist account, where probabilities are degrees of belief. | |
| From: Mark Colyvan (Introduction to the Philosophy of Mathematics [2012], 9.1.8) | |
| A reaction: [compressed] |
| 17939 | Mathematics can reveal structural similarities in diverse systems [Colyvan] |
| Full Idea: Mathematics can demonstrate structural similarities between systems (e.g. missing population periods and the gaps in the rings of Saturn). | |
| From: Mark Colyvan (Introduction to the Philosophy of Mathematics [2012], 6.3.2) | |
| A reaction: [Colyvan expounds the details of his two examples] It is these sorts of results that get people enthusiastic about the mathematics embedded in nature. A misunderstanding, I think. |
| 17938 | Mathematics can show why some surprising events have to occur [Colyvan] |
| Full Idea: Mathematics can show that under a broad range of conditions, something initially surprising must occur (e.g. the hexagonal structure of honeycomb). | |
| From: Mark Colyvan (Introduction to the Philosophy of Mathematics [2012], 6.3.2) |
| 17934 | Proof by cases (by 'exhaustion') is said to be unexplanatory [Colyvan] |
| Full Idea: Another style of proof often cited as unexplanatory are brute-force methods such as proof by cases (or proof by exhaustion). | |
| From: Mark Colyvan (Introduction to the Philosophy of Mathematics [2012], 5.2.1) |
| 17933 | Reductio proofs do not seem to be very explanatory [Colyvan] |
| Full Idea: One kind of proof that is thought to be unexplanatory is the 'reductio' proof. | |
| From: Mark Colyvan (Introduction to the Philosophy of Mathematics [2012], 5.2.1) | |
| A reaction: Presumably you generate a contradiction, but are given no indication of why the contradiction has arisen? Tracking back might reveal the source of the problem? Colyvan thinks reductio can be explanatory. |
| 17935 | If inductive proofs hold because of the structure of natural numbers, they may explain theorems [Colyvan] |
| Full Idea: It might be argued that any proof by induction is revealing the explanation of the theorem, namely, that it holds by virtue of the structure of the natural numbers. | |
| From: Mark Colyvan (Introduction to the Philosophy of Mathematics [2012], 5.2.1) | |
| A reaction: This is because induction characterises the natural numbers, in the Peano Axioms. |
| 17942 | Can a proof that no one understands (of the four-colour theorem) really be a proof? [Colyvan] |
| Full Idea: The proof of the four-colour theorem raises questions about whether a 'proof' that no one understands is a proof. | |
| From: Mark Colyvan (Introduction to the Philosophy of Mathematics [2012], 9.1.6) | |
| A reaction: The point is that the theorem (that you can colour countries on a map with just four colours) was proved with the help of a computer. |
| 17937 | Mathematical generalisation is by extending a system, or by abstracting away from it [Colyvan] |
| Full Idea: One type of generalisation in mathematics extends a system to go beyond what is was originally set up for; another kind involves abstracting away from some details in order to capture similarities between different systems. | |
| From: Mark Colyvan (Introduction to the Philosophy of Mathematics [2012], 5.2.2) |
| 5901 | Is 'productive of happiness' the definition of 'right', or the cause of it? [Ross on Bentham] |
| Full Idea: Bentham has not made up his mind whether he thinks that 'right' means 'productive of the general happiness', or that being productive of the general happiness is what makes acts right (and he would have thought the difference unimportant). | |
| From: comment on Jeremy Bentham (Intro to Principles of Morals and Legislation [1789]) by W. David Ross - The Right and the Good §I | |
| A reaction: The issue is whether rightness exists as a concept separate from happiness. I take it Bentham would vote for the first reading, as he has no interest in what is right, apart from increasing happiness. |
| 5271 | Prejudice apart, push-pin has equal value with music and poetry [Bentham] |
| Full Idea: Prejudice apart, the game of push-pin is of equal value with the arts and science of music and poetry. | |
| From: Jeremy Bentham (Constitutional Code I [1827], p.139), quoted by J.R. Dinwiddy - Bentham p.114 | |
| A reaction: Mill quoted this with implied outrage, but Bentham was attacking public subsidies to the arts when he said it. It is a basic idea in the debate on pleasure - that pleasures are only distinguished by their intensity, not some other value. |
| 5934 | Of Bentham's 'dimensions' of pleasure, only intensity and duration matter [Ross on Bentham] |
| Full Idea: Most of Bentham's 'dimensions' of pleasure refer to further pleasures, or are irrelevant to the pleasure; we are left with intensity and duration as the characteristics on which depend the value of a pleasure qua pleasure, and there is nothing to add. | |
| From: comment on Jeremy Bentham (Intro to Principles of Morals and Legislation [1789]) by W. David Ross - The Right and the Good §VI | |
| A reaction: I agree. When Bentham produces his list he seems to be trying to add a bogus enrichment to what is really a rather crude and basic notion of the aim of life. Your simple hedonist appears to only desire high intensity and long duration. |
| 3777 | Pleasure and pain control all human desires and duties [Bentham] |
| Full Idea: Nature has placed mankind under the governance of two sovereign masters, pain and pleasure. It is for them alone to point out what we ought to do, as well as to determine what we shall do. | |
| From: Jeremy Bentham (Intro to Principles of Morals and Legislation [1789], I.1) | |
| A reaction: Ridiculous. Both halves are false. We pursue things for other reasons, and to deny this makes his idea a tautology. Deep ecology has nothing to do with human pleasure or pain. |
| 3554 | Bentham thinks happiness is feeling good, but why use morality to achieve that? [Annas on Bentham] |
| Full Idea: It is easy to fall into Bentham's mindless assumption that happiness must be a specific state of feeling good about something, but it is mysterious why anyone would think morality a good strategy for achieving this. | |
| From: comment on Jeremy Bentham (Intro to Principles of Morals and Legislation [1789]) by Julia Annas - The Morality of Happiness 2.7 |
| 3781 | The value of pleasures and pains is their force [Bentham] |
| Full Idea: It behoves the legislator to understand the force of pleasures and pains, which is their value. | |
| From: Jeremy Bentham (Intro to Principles of Morals and Legislation [1789], IV.1) |
| 20977 | Natural rights are nonsense, and unspecified natural rights is nonsense on stilts [Bentham] |
| Full Idea: Natural rights is simple nonsense: natural and imprescriptible rights, rhetorical nonsense — nonsense upon stilts. | |
| From: Jeremy Bentham (Anarchical Fallacies: on the Declaration of Rights [1796]) | |
| A reaction: If you want your opinion to be remembered, express it memorably! I take natural rights to be the basic principles and values which are obvious to almost everyone when they come for formulate legal rights (which are the only true rights). |
| 3778 | The community's interest is a sum of individual interests [Bentham] |
| Full Idea: The interest of the community is the sum of the interests of the several members who compose it. | |
| From: Jeremy Bentham (Intro to Principles of Morals and Legislation [1789], I.4) |
| 21006 | If women share rights with men, they will exhibit similar virtues [Wollstonecraft] |
| Full Idea: Let woman share the rights and she will emulate the virtues of man; for she must grow more perfect when emancipated, or justify that authority that chains such a weak being to her duty. | |
| From: Mary Wollstonecraft (Vindication of the Rights of Women [1792], p.294), quoted by Amartya Sen - The Idea of Justice 18 'Wrath' | |
| A reaction: Presumably this implies that if emancipation led to women exceeding men in such virtues, there would be some justification for imposing the chains on the men rather than the women. Consider wars. Probably best to just abandon chains. |
| 21003 | Only laws can produce real rights; rights from 'law of nature' are imaginary [Bentham] |
| Full Idea: Right, the substantive right, is the child of law; from real laws come real rights; but from imaginary laws, from 'law of nature' can come only imaginary rights. | |
| From: Jeremy Bentham (Anarchical Fallacies: on the Declaration of Rights [1796], II.523), quoted by Amartya Sen - The Idea of Justice 17 'Ethics' | |
| A reaction: I am coming to agree with this. What are called 'natural rights' are just self-evident good reasons why someone should be allowed a right. A right can, of course, come from an informal agreement. The question is: why award that particular legal right? |
| 20280 | Large mature animals are more rational than babies. But all that really matters is - can they suffer? [Bentham] |
| Full Idea: A full-grown horse or dog is beyond comparison a more rational animal than an infant of a day, or even a month, old. But suppose they be otherwise, what would it avail? The question is not, Can they reason? nor Can they talk? but, Can they suffer? | |
| From: Jeremy Bentham (Intro to Principles of Morals and Legislation [1789], XVIII 1 n), quoted by Peter Singer - Practical Ethics 03 | |
| A reaction: This is certainly an inspiring, and even shocking question, which never seems to have been so directly asked before in the entire history of European thought. Awesome. |
| 3779 | Unnatural, when it means anything, means infrequent [Bentham] |
| Full Idea: Unnatural, when it means anything, means unfrequent. | |
| From: Jeremy Bentham (Intro to Principles of Morals and Legislation [1789], II.14 n8.9) |
| 3780 | We must judge a thing morally to know if it conforms to God's will [Bentham] |
| Full Idea: It is necessary to know first whether a thing is right in order to know from thence whether it be conformable to the will of God. | |
| From: Jeremy Bentham (Intro to Principles of Morals and Legislation [1789], II.18) |