| 483 | Start a thesis with something undisputable [Diogenes of Apollonia] |
| Full Idea: In starting any thesis, it seems to me, one should put forward as one's point of departure something incontrovertible. | |
| From: Diogenes (Apoll) (fragments/reports [c.440 BCE], B01), quoted by Diogenes Laertius - Lives of Eminent Philosophers 09.57 |
| 23356 | Self-evidence is most obvious when people who deny a proposition still have to use it [Epictetus] |
| Full Idea: It is about the strongest proof one could offer of a proposition being evident, that even he who contradicts it finds himself having to make use of it. | |
| From: Epictetus (The Discourses [c.56], 2.20.01) | |
| A reaction: Philosophers sometimes make fools of themselves by trying, by the use of elaborate sophistry, to demolish propositions which are self-evidently true. Don't be one of these philosophers! |
| 21249 | Some things are self-evident to us; others are only self-evident in themselves [Aquinas] |
| Full Idea: A thing can be self-evident in either of two ways: on the one hand, self-evident in itself, though not to us; on the other hand, self-evident in itself, and to us. | |
| From: Thomas Aquinas (Summa Theologicae [1265], Art 1, Obj 3) | |
| A reaction: A clear distinction, which is hard to deny, though there are lots of borderline cases. Self-evident to genius, and self-evident to future genius. Self-evident to almost everyone. Goldbach's Conjecture may be self-evident but unknowable. |
| 22128 | Augustine's 'illumination' theory of knowledge leads to nothing but scepticism [Duns Scotus, by Dumont] |
| Full Idea: Scotus rejected Henry of Ghent's defence of Augustine's of knowledge by 'illumination', as leading to nothing but scepticism. ...After this, illumination never made a serious recovery. | |
| From: report of John Duns Scotus (works [1301]) by Stephen D. Dumont - Duns Scotus p.206 |
| 24025 | Clear and distinct truths must be known all at once (unlike deductions) [Descartes] |
| Full Idea: We require two conditions for intuition, namely that the proposition appear clear and distinct, and then that it be understood all at once and not successively. Deduction, on the other hand, implies a certain movement of the mind. | |
| From: René Descartes (Rules for the Direction of the Mind [1628], 11) | |
| A reaction: A nice distinction. Presumably with deduction you grasp each step clearly, and then the inference and conclusion, and you can then forget the previous steps because you have something secure. |
| 21253 | Descartes needs to demonstrate how other people can attain his clear and distinct conceptions [Leibniz] |
| Full Idea: It is not sufficient for Descartes to claim that he perceives something in himself clearly and distinctly, for this is to not complete the demonstration, unless he shows the method through which others can attain the same experience. | |
| From: Gottfried Leibniz (New Essays on Human Understanding [1704], App X) | |
| A reaction: For the simplest rational insight this seems a rather tough requirement. If you say A>B, and B>C, so A>C, then once you have grasped the concept of 'greater than' I'm not sure there is a further possible demonstration. |
| 23635 | Truths are self-evident to sensible persons who understand them clearly without prejudice [Reid] |
| Full Idea: Self-evident propositions are those which appear evident to every man of sound understanding who apprehends the meaning of them distinctly, and attends to them without prejudice. | |
| From: Thomas Reid (Essays on Intellectual Powers 2: Senses [1785], 10) | |
| A reaction: I suspect that there are some truths which are self-evident to dogs. There are also truths which are self-evident to experts, but not to ordinary persons of good understanding. Self-evidence is somewhat contextual. Self-evidence can be empirical. |
| 9348 | Experienceless bodies have space; propertyless bodies have substance; this must be seen a priori [Kant] |
| Full Idea: Remove from your experiential concept of a body everything empirical (colour, hardness etc), and there still remains its space. If you remove all the properties which experience teaches you, there remains substance. This shows your a priori faculty. | |
| From: Immanuel Kant (Critique of Pure Reason [1781], B006) | |
| A reaction: Presumably you can also 'remove' the space and the substance. Maybe there are no actual items such as spaces or substances, so getting both of them wrong wouldn't be a good advertisement for the faculty. It's just imagination? |
| 8657 | Mathematicians just accept self-evidence, whether it is logical or intuitive [Frege] |
| Full Idea: The mathematician rests content if every transition to a fresh judgement is self-evidently correct, without enquiring into the nature of this self-evidence, whether it is logical or intuitive. | |
| From: Gottlob Frege (Grundlagen der Arithmetik (Foundations) [1884], §90) | |
| A reaction: Note the suggestion that there are two different sorts of self-evidence. But see Idea 1410. Frege presumably drifted into philosophy because he wasn't happy with this blissful ignorance. |
| 16887 | Frege's concept of 'self-evident' makes no reference to minds [Frege, by Burge] |
| Full Idea: Frege's terms that translate 'self-evident' usually make no explicit reference to actual minds. | |
| From: report of Gottlob Frege (works [1890]) by Tyler Burge - Frege on Knowing the Foundations 4 | |
| A reaction: This follows the distinction in Aquinas, between things that are intrinsically self-evident, and things that are self-evident to particular people. God, presumably, knows all of the former. |
| 22205 | Feelings of self-evidence (and necessity) are just the inventions of theory [Husserl] |
| Full Idea: So-called feelings of self-evidence, of intellectual necessity, and however they may otherwise be called, are just theoretically invented feelings. | |
| From: Edmund Husserl (Ideas: intro to pure phenomenology [1913], I.2.021) | |
| A reaction: This seems to be a dismissal of the a priori necessary on the grounds that it is 'theory-laden' - which is why it has to be bracketed in order to do phenomenology. |
| 21216 | Husserl says we have intellectual intuitions (of categories), as well as of the senses [Husserl, by Velarde-Mayol] |
| Full Idea: The novelty of Husserl is to describe that we have intellectual intuitions, intuitions of categories as we have intuitions of sense objects. | |
| From: report of Edmund Husserl (Logical Investigations [1900], II.VI.24) by Victor Velarde-Mayol - On Husserl 2.4.4 | |
| A reaction: This is 'intuitions' in Kant's sense, of something like direct apprehensions. This idea is an axiom of phenomenology, because all mental life must be bracketed, and not just the sense experience part. |
| 7554 | Self-evidence is often a mere will-o'-the-wisp [Russell] |
| Full Idea: Self-evidence is often a mere will-o'-the-wisp, which is sure to lead us astray if we take it as our guide. | |
| From: Bertrand Russell (Mathematics and the Metaphysicians [1901], p.78) | |
| A reaction: The sort of nice crisp remark you would expect from a good empiricist philosopher. Compare Idea 4948. However Russell qualifies it with the word 'often', and all philosophers eventually realise that you have to start somewhere. |
| 5412 | Some propositions are self-evident, but their implications may also be self-evident [Russell] |
| Full Idea: When a certain number of logical principles have been admitted as self-evident, the rest can be deduced from them; but the propositions deduced are often just as self-evident as those that were assumed without proof. | |
| From: Bertrand Russell (Problems of Philosophy [1912], Ch.11) | |
| A reaction: This seems an important corrective to the traditional rationalist dream, based on Euclid, that all knowledge is self-evident axioms followed by proofs of the rest. But Russell here endorses a more sensible sort of rationalism. |
| 5413 | Particular instances are more clearly self-evident than any general principles [Russell] |
| Full Idea: Particular instances are more self-evident than general principles; for example, the law of contradiction is evident as soon as it is understood, but it is not as evident as that a particular rose cannot be both red and not red. | |
| From: Bertrand Russell (Problems of Philosophy [1912], Ch.11) | |
| A reaction: This seems to true about nearly all reasoning, because whenever we are faced with a general principle for assessment, we check it by testing it against a series of particular instances, and try to think of contradictory particular counterexamples. |
| 5415 | As shown by memory, self-evidence comes in degrees [Russell] |
| Full Idea: It is clear from the case of memory that self-evidence has degrees, and is present in gradations ranging from absolute certainty down to an almost imperceptible faintness. | |
| From: Bertrand Russell (Problems of Philosophy [1912], Ch.11) | |
| A reaction: I am beginning to see Russell as the 'father of modern rationalism'. His relaxation of notions of an all-or-nothing a priori, and of a sharp distinction between axioms and proofs, lead to a sensible rationalism which even a Humean sceptic might buy. |
| 5416 | If self-evidence has degrees, we should accept the more self-evident as correct [Russell] |
| Full Idea: If propositions can have some degree of self-evidence without being true, we must say, where there is a conflict, that the more self-evident proposition is to be retained and the less self-evident rejected. | |
| From: Bertrand Russell (Problems of Philosophy [1912], Ch.11) | |
| A reaction: This is a key part of Russell's 'moderate rationalism'. Presumably the rejected propositions were therefore not self-evident, and can be used as training for intuitions, by seeing why we got it wrong. Fools find absurd falsehoods self-evidently true. |
| 16907 | If the truth doesn't follow from self-evidence, then self-evidence cannot justify a truth [Wittgenstein] |
| Full Idea: If the truth of a proposition does not follow from the fact that it is self-evident to us, then its self-evidence in no way justifies our belief in its truth. | |
| From: Ludwig Wittgenstein (Tractatus Logico-Philosophicus [1921], 5.1363), quoted by Robin Jeshion - Frege's Notion of Self-Evidence 4 | |
| A reaction: Frege seems to have taken self-evidence as intrinsic justification, but Wittgenstein seems to demand a supporting inference. But what is it all based on? Stipulative definitions? |
| 9379 | A sentence is obvious if it is true, and any speaker of the language will instantly agree to it [Quine] |
| Full Idea: A sentence is obvious if (a) it is true and (b) any speaker of the language is prepared, for any reason or none, to assent to it without hesitation, unless put off by being asked so obvious a question. | |
| From: Willard Quine (Reply to Hellman [1975], p.206), quoted by Paul Boghossian - Analyticity Reconsidered §III | |
| A reaction: This comes from someone who is keen to deny a priori knowledge, but what are we to make of the expostulations "It's obvious, you idiot!", and "Now I see it, it's obvious!", and "It seemed obvious, but I was wrong!"? |
| 8887 | It is hard to give the concept of 'self-evident' a clear and defensible characterization [Bonjour] |
| Full Idea: Foundationalists find it difficult to attach a clear and defensible content to the idea that basic beliefs that are characterized as 'self-justified' or 'self-evident'. | |
| From: Laurence Bonjour (A Version of Internalist Foundationalism [2003], 1.4) | |
| A reaction: A little surprising from a fan of a priori foundations, especially given that 'self-evident' is common usage, and not just philosophers' jargon. I think we can talk of self-evidence without a precise definition. We talk of an 'ocean' without trouble. |
| 13480 | Fregean self-evidence is an intrinsic property of basic truths, rules and definitions [Hart,WD] |
| Full Idea: The conception of Frege is that self-evidence is an intrinsic property of the basic truths, rules, and thoughts expressed by definitions. | |
| From: William D. Hart (The Evolution of Logic [2010], p.350) | |
| A reaction: The problem is always that what appears to be self-evident may turn out to be wrong. Presumably the effort of arriving at a definition ought to clarify and support the self-evident ingredient. |
| 6414 | Two propositions might seem self-evident, but contradict one another [Grayling] |
| Full Idea: Two propositions might contradict each other despite appearing self-evident when considered separately. | |
| From: A.C. Grayling (Russell [1996], Ch.2) | |
| A reaction: Russell's proposal (Idea 5416) is important here, that self-evidence comes in degrees. If self-evidence was all-or-nothing, Grayling's point would be a major problem, but it isn't. Bonjour explores the idea more fully (e.g. Idea 3704) |
| 9597 | There are 'armchair' truths which are not a priori, because experience was involved [Williamson] |
| Full Idea: There is extensive 'armchair knowledge' in which experience plays no strictly evidential role, but it may not fit the stereotype of the a priori, because the contribution of experience was more than enabling, such as armchair truths about our environment. | |
| From: Timothy Williamson (The Philosophy of Philosophy [2007], 5.5) | |
| A reaction: Once this point is conceded we have no idea where to draw the line. Does 'if it is red it can't be green' derive from experience? I think it might. |