12 ideas
| 15717 | Using Choice, you can cut up a small ball and make an enormous one from the pieces [Kaplan/Kaplan] |
| Full Idea: The problem with the Axiom of Choice is that it allows an initiate (by an ingenious train of reasoning) to cut a golf ball into a finite number of pieces and put them together again to make a globe as big as the sun. | |
| From: R Kaplan / E Kaplan (The Art of the Infinite [2003], 9) | |
| A reaction: I'm not sure how this works (and I think it was proposed by the young Tarski), but it sounds like a real problem to me, for all the modern assumptions that Choice is fine. |
| 15712 | 1 and 0, then add for naturals, subtract for negatives, divide for rationals, take roots for irrationals [Kaplan/Kaplan] |
| Full Idea: You have 1 and 0, something and nothing. Adding gives us the naturals. Subtracting brings the negatives into light; dividing, the rationals; only with a new operation, taking of roots, do the irrationals show themselves. | |
| From: R Kaplan / E Kaplan (The Art of the Infinite [2003], 1 'Mind') | |
| A reaction: The suggestion is constructivist, I suppose - that it is only operations that produce numbers. They go on to show that complex numbers don't quite fit the pattern. |
| 15711 | The rationals are everywhere - the irrationals are everywhere else [Kaplan/Kaplan] |
| Full Idea: The rationals are everywhere - the irrationals are everywhere else. | |
| From: R Kaplan / E Kaplan (The Art of the Infinite [2003], 1 'Nameless') | |
| A reaction: Nice. That is, the rationals may be dense (you can always find another one in any gap), but the irrationals are continuous (no gaps). |
| 15714 | 'Commutative' laws say order makes no difference; 'associative' laws say groupings make no difference [Kaplan/Kaplan] |
| Full Idea: The 'commutative' laws say the order in which you add or multiply two numbers makes no difference; ...the 'associative' laws declare that regrouping couldn't change a sum or product (e.g. a+(b+c)=(a+b)+c ). | |
| From: R Kaplan / E Kaplan (The Art of the Infinite [2003], 2 'Tablets') | |
| A reaction: This seem utterly self-evident, but in more complex systems they can break down, so it is worth being conscious of them. |
| 15715 | 'Distributive' laws say if you add then multiply, or multiply then add, you get the same result [Kaplan/Kaplan] |
| Full Idea: The 'distributive' law says you will get the same result if you first add two numbers, and then multiply them by a third, or first multiply each by the third and then add the results (i.e. a · (b+c) = a · b + a · c ). | |
| From: R Kaplan / E Kaplan (The Art of the Infinite [2003], 2 'Tablets') | |
| A reaction: Obviously this will depend on getting the brackets right, to ensure you are indeed doing the same operations both ways. |
| 15713 | The first million numbers confirm that no number is greater than a million [Kaplan/Kaplan] |
| Full Idea: The claim that no number is greater than a million is confirmed by the first million test cases. | |
| From: R Kaplan / E Kaplan (The Art of the Infinite [2003], 2 'Intro') | |
| A reaction: Extrapolate from this, and you can have as large a number of cases as you could possibly think of failing to do the inductive job. Love it! Induction isn't about accumulations of cases. It is about explanation, which is about essence. Yes! |
| 4581 | Virtues and vices are like secondary qualities in perception, found in observers, not objects [Hume] |
| Full Idea: Vice and virtue may be compared to sounds, colours, heat and cold, which, according to modern philosophy, are not qualities in objects but perceptions in the mind. | |
| From: David Hume (Letters [1739], to Hutcheson 1740) | |
| A reaction: Very revealing about the origin of the is/ought idea, but this is an assertion rather than an argument. Most Greeks treat value as a primary quality of things (e.g. life, harmony, beauty, health). |
| 4580 | All virtues benefit either the public, or the individual who possesses them [Hume] |
| Full Idea: I desire you to consider if there be any quality that is virtuous, without having a tendency either to the public good or to the good of the person who possesses it. | |
| From: David Hume (Letters [1739], to Hutcheson 1739) | |
| A reaction: Obviously this is generally true. How, though, does it benefit the individual to secretly preserve their integrity? I go round to visit a friend to repay a debt; I am told they have died; I quietly leave some money on the table and leave. Why? |
| 13304 | Learned men gain more in one day than others do in a lifetime [Posidonius] |
| Full Idea: In a single day there lies open to men of learning more than there ever does to the unenlightened in the longest of lifetimes. | |
| From: Posidonius (fragments/reports [c.95 BCE]), quoted by Seneca the Younger - Letters from a Stoic 078 | |
| A reaction: These remarks endorsing the infinite superiority of the educated to the uneducated seem to have been popular in late antiquity. It tends to be the religions which discourage great learning, especially in their emphasis on a single book. |
| 4579 | The idea of a final cause is very uncertain and unphilosophical [Hume] |
| Full Idea: Your sense of 'natural' is founded on final causes, which is a consideration that appears to me pretty uncertain and unphilosophical. | |
| From: David Hume (Letters [1739], to Hutcheson 1739) | |
| A reaction: This is the rejection of Aristotelian teleology by modern science. I agree that the notion of utterly ultimate final cause is worse than 'uncertain' - it is an impossible concept. Nevertheless, I prefer Aristotle to Hume. Nature can teach us lessons. |
| 20705 | That events could be uncaused is absurd; I only say intuition and demonstration don't show this [Hume] |
| Full Idea: I never asserted so absurd a proposition as that anything might arise without a cause: I only maintained that our certainty of the falsehood of that proposition proceeded neither from intuition nor from demonstration, but from another source. | |
| From: David Hume (Letters [1739], 1754), quoted by Brian Davies - Introduction to the Philosophy of Religion 5 'God' | |
| A reaction: Since the other source is habit, he is being a bit disingenuous. While rational intuition and demonstration give a fairly secure basis for the universality of causation, mere human habits of expectation give very feeble grounds. |
| 20820 | Time is an interval of motion, or the measure of speed [Posidonius, by Stobaeus] |
| Full Idea: Posidonius defined time thus: it is an interval of motion, or the measure of speed and slowness. | |
| From: report of Posidonius (fragments/reports [c.95 BCE]) by John Stobaeus - Anthology 1.08.42 | |
| A reaction: Hm. Can we define motion or speed without alluding to time? Looks like we have to define them as a conjoined pair, which means we cannot fully understand either of them. |