| 2301 | We know by thought that what is done cannot be undone [Descartes] |
| Full Idea: Some ideas belong exclusively to the mind, such as perceiving that what has been done cannot be undone, and everything else that is known by the light of nature. | |
| From: René Descartes (Meditations [1641], §6.82) |
| 12553 | Some of our ideas contain relations which we cannot conceive to be absent [Locke] |
| Full Idea: In some of our ideas there are certain relations, habitudes, and connexions, so visibly included in the nature of the ideas themselves, that we cannot conceive them separable from them, by any power whatsoever. | |
| From: John Locke (Essay Conc Human Understanding (2nd Ed) [1694], 4.03.29) | |
| A reaction: This is the conceptual version of a priori necessity. The question then becomes whether this necessity can be traced back to reality, or merely to conventions which created the ideas in the first place. Analytic philosophy likes this idea. |
| 2112 | Truths of reason are known by analysis, and are necessary; facts are contingent, and their opposites possible [Leibniz] |
| Full Idea: There are two kinds of truths: of reasoning and of facts. Truths of reasoning are necessary and their opposites impossible. Facts are contingent and their opposites possible. A necessary truth is known by analysis. | |
| From: Gottfried Leibniz (Monadology [1716], §33) |
| 17079 | Proofs of necessity come from the understanding, where they have their source [Leibniz] |
| Full Idea: The fundamental proof of necessary truths comes from the understanding alone, and other truths come from experience or from observations of the senses. Our mind is capable of knowing truths of both sorts, but it is the source of the former. | |
| From: Gottfried Leibniz (New Essays on Human Understanding [1704], 1.01) | |
| A reaction: Interesting because it not only spells out that necessary truths are known a priori, but also explicitly says that the understanding is the 'source' of the truths, or at least the source of their proofs. He also says possibilities derive from essences. |
| 19432 | Intelligible truth is independent of any external things or experiences [Leibniz] |
| Full Idea: Intelligible truth is independent of the truth or of the existence outside us of sensible and material things. ....It is generally true that we only know necessary truths by the natural light [of reason] | |
| From: Gottfried Leibniz (Letters to Queen Charlotte [1702], 1702) | |
| A reaction: A nice quotation summarising a view for which Leibniz is famous - that there is a tight correlation between necessary truths and our a priori knowledge of them. The obvious challenge comes from Kripke's claim that scientists can discover necessities. |
| 23461 | Kant thought worldly necessities are revealed by what maths needs to make sense [Kant, by Morris,M] |
| Full Idea: It struck Kant (to put it crudely) that there are some things which are necessarily true of the world, revealed when we consider what is required for mathematics - indeed, thinking in general - to make sense. | |
| From: report of Immanuel Kant (Critique of Pure Reason [1781]) by Michael Morris - Guidebook to Wittgenstein's Tractatus Intro | |
| A reaction: This is given as background the Wittgenstein's Tractatus. He disagrees with Kant because logic is not synthetic. I see a strong connection with the stoic belief that the natural world is intrinsically rational. |
| 14710 | Necessity is always knowable a priori, and what is known a priori is always necessary [Kant, by Schroeter] |
| Full Idea: The Kantian rationalist view is that what is necessary is always knowable a priori, and what is knowable a priori is always necessary. | |
| From: report of Immanuel Kant (Critique of Pure Reason [1781]) by Laura Schroeter - Two-Dimensional Semantics 2.3.1 | |
| A reaction: Nice to get a clear spelling out of the two-way relationship here. Why couldn't Kant put it as clearly as this? See Kripke for the first big challenges to Kant's picture. I like aposteriori necessities. |
| 16256 | For Kant metaphysics must be necessary, so a priori, so can't be justified by experience [Kant, by Maudlin] |
| Full Idea: Kant maintained that metaphysics must be a body of necessary truths, and that necessary truths must be a priori, so metaphysical claims could not be justified by experience. | |
| From: report of Immanuel Kant (Critique of Pure Reason [1781]) by Tim Maudlin - The Metaphysics within Physics 3 | |
| A reaction: I'm coming to the view that there is no a priori necessity, and that all necessities are entailments from the nature of reality. The apparent a priori necessities are just at a very high level of abstraction. |
| 5524 | Maths must be a priori because it is necessary, and that cannot be derived from experience [Kant] |
| Full Idea: Mathematical propositions are always a priori judgments and are never empirical, because they carry necessity with them, which cannot be derived from experience. | |
| From: Immanuel Kant (Critique of Pure Reason [1781], B014) | |
| A reaction: Personally I like the idea that maths is the 'science of patterns', but then I take it that the features of patterns will be common to all possible worlds. Presumably a proposition could be contingent, and yet true in all possible worlds. |
| 23495 | The tautologies of logic show the logic of language and the world [Wittgenstein] |
| Full Idea: The fact that the propositions of logic are tautologies shows the formal - logical - properties of language and the world. | |
| From: Ludwig Wittgenstein (Tractatus Logico-Philosophicus [1921], 6.12) | |
| A reaction: This seems to me an extraordinarily hubristic remark (philosophically speaking), especially coming from a work which famously throws away its own ladder. He is very much pursuing Kant's project. |
| 9169 | A statement can be metaphysically necessary and epistemologically contingent [Putnam] |
| Full Idea: A statement can be (metaphysically) necessary and epistemologically contingent. Human intuition has no privileged access to metaphysical necessity. | |
| From: Hilary Putnam (Meaning and Reference [1973], p.160) | |
| A reaction: The terminology here is dangerously confusing. 'Contingent' is a term which (as Kripke insists) refers to reality, not to our epistemological abilities. The locution of adding the phrase "for all I know" seems to handle the problem better. |
| 15101 | Once you give up necessity as a priori, causal necessity becomes the main type of necessity [Shoemaker] |
| Full Idea: Once the obstacle of the deeply rooted conviction that necessary truths should be knowable a priori is removed, ...causal necessity is (pretheoretically) the very paradigm of necessity, in ordinary usage and in dictionaries. | |
| From: Sydney Shoemaker (Causal and Metaphysical Necessity [1998], VII) | |
| A reaction: The a priori route seems to lead to logical necessity, just by doing a priori logic, and also to metaphysical necessity, by some sort of intuitive vision. This is a powerful idea of Shoemaker's (implied, of course, in Kripke). |
| 4728 | Kripke separates necessary and a priori, proposing necessary a posteriori and contingent a priori examples [Kripke, by O'Grady] |
| Full Idea: It is now recognised that the apriori and the necessary don't always have to go together, ..and Kripke has suggested examples of necessary-aposteriori and contingent-apriori beliefs. | |
| From: report of Saul A. Kripke (Naming and Necessity lectures [1970]) by Paul O'Grady - Relativism Ch.4 | |
| A reaction: The simple point is that whether something is necessary or contingent is a quite separate question from how we come to know that they are. There isn't a new mode of reality called 'necessary a posteriori'. |
| 16990 | A priori = Necessary because we imagine all worlds, and we know without looking at actuality? [Kripke] |
| Full Idea: People think 'necessary' and 'a priori' mean the same for two reasons: we can assess what is feasible in all possible world by running them through our heads, and something known a priori avoids looking at the world, so it must be necessary. | |
| From: Saul A. Kripke (Naming and Necessity lectures [1970], Lecture 1) | |
| A reaction: [compressed] Kripke denies this doctrine, and pulls the concepts apart. Kant seems to be the chief representative of the view he is attacking. Hossack defends the older view. |
| 15228 | Necessity and contingency are separate from the a priori and the a posteriori [Harré/Madden] |
| Full Idea: The concepts of necessity and contingency are detached from those of the apriori and the a posteriori. | |
| From: Harré,R./Madden,E.H. (Causal Powers [1975], 1.IV) | |
| A reaction: This seems to arise quite independently of Kripke, from the attack by the authors on the Humean view of modality. They also mention the possibility of the apriori contingent. |
| 2526 | Philosophers regularly confuse failures of imagination with insights into necessity [Dennett] |
| Full Idea: The besetting foible of philosophers is mistaking failures of imagination for insights into necessity. | |
| From: Daniel C. Dennett (Brainchildren [1998], Ch.25) |
| 12428 | Many necessities are inexpressible, and unknowable a priori [Kitcher] |
| Full Idea: There are plenty of necessary truths that we are unable to express, let alone know a priori. | |
| From: Philip Kitcher (A Priori Knowledge Revisited [2000], §II) | |
| A reaction: This certainly seems to put paid to any simplistic idea that the a priori and the necessary are totally coextensive. We might, I suppose, claim that all necessities are a priori for the Archangel Gabriel (or even a very bright cherub). Cf. Idea 12429. |
| 20476 | If the necessary is a priori, so is the contingent, because the same evidence is involved [Casullo] |
| Full Idea: If one can only know a priori that a proposition is necessary, then one can know only a priori that a proposition is contingent. The evidence relevant to determining the latter is the same as that relevant to determining the former. | |
| From: Albert Casullo (A Priori Knowledge [2002], 3.2) | |
| A reaction: This seems a telling point, but I suppose it is obvious. If you see that the cat is on the mat, nothing in the situation tells you whether this is contingent or necessary. We assume it is contingent, but that may be an a priori assumption. |
| 13956 | Kripke is often taken to be challenging a priori insights into necessity [Chalmers] |
| Full Idea: At various points in this book, I use a priori methods to gain insight into necessity; this is the sort of thing that Kripke's account is often taken to challenge. | |
| From: David J.Chalmers (The Conscious Mind [1996], 1.2.4) | |
| A reaction: Chalmers uses his 2-D approach to split off an a priori part from Kripke's a posterior part of our insight into necessity. |
| 9598 | Modal thinking isn't a special intuition; it is part of ordinary counterfactual thinking [Williamson] |
| Full Idea: The epistemology of metaphysical modality requires no dedicated faculty of intuition. It is simply a special case of the epistemology of counterfactual thinking, a kind of thinking tightly integrated with our thinking about the spatio-temporal world. | |
| From: Timothy Williamson (The Philosophy of Philosophy [2007], 5.6) | |
| A reaction: This seems to me to be spot-on, though it puts the focus increasingly on the faculty of imagination, as arguably an even more extraordinary feature of brains than the much-vaunted normal consciousness. |
| 21621 | We can't infer metaphysical necessities to be a priori knowable - or indeed knowable in any way [Williamson] |
| Full Idea: The inference from metaphysical necessity to a priori knowlability is, as Kripke has emphasized, fallacious. Indeed, metaphysical necessities cannot be assumed knowable in any way at all. | |
| From: Timothy Williamson (Vagueness [1994], 7.4) | |
| A reaction: The second sentence sounds like common sense. He cites Goldbach's Conjecture. A nice case of the procedural rule of keeping your ontology firmly separated from your epistemology. How is it? is not How do we know it? |
| 4719 | Maybe developments in logic and geometry have shown that the a priori may be relative [O'Grady] |
| Full Idea: A weaker form of relativism holds that developments in logic, in maths and in geometry have shown how a relativised notion of the a priori is possible. | |
| From: Paul O'Grady (Relativism [2002], Ch.4) | |
| A reaction: This is non-Euclidean geometry, and multiple formalisations of logic. Personally I don't believe it. You can expand these subjects, and pursue whimsical speculations, but I have faith in their stable natural core. Neo-Platonism. |