• numberjohnny5
    I have been struggling to make clear systematic distinctions between these terms, and I'm hoping someone can help. So, what are the differences and/or similarities between:

    (a) analytic truth
    (b) a priori truth
    (c) logical necessity
    (d) absolute certainty
    (e) metaphysical necessity
    (f) ontological necessity

    I take (a) to be comprised of (b) and (c).
    I take (e) and (f) to be identical.

    Is that accurate?

    Also, is (d) similar or identical to (c)?
  • Fafner
    (a) analytic truth: truth by virtue of meaning (like "red is a color" or "all bachelors are unmarried").

    (b) a priori truth: something you can know (=being justified to believe) independently of sense experience (like that 2+2=4).

    (c) logical necessity: true by virtue of the syntactical or formal features of linguistic expressions (i.e., in a case of a tautology like "either p is true or false")

    (d) absolute certainty: having evidence in favor of a proposition p that logically guarantee the truth p. alternative explanation: having evidence for p that cannot be defeated by any further counter evidence (and again the 'can't' here is logically necessary).

    (e) metaphysical necessity: (controversial - some people think there's no meaningful distinction between this and logical necessity) a proposition which is true in all possible worlds, which is not tautological in form. (the "true in all possible worlds" definition also applies to logical necessity, but it is not sufficient for distinguishing it from metaphysical necessity, if you believe that they are different things)

    (f) ontological necessity: I'm not familiar with this notion, but maybe it means metaphysical essence, i.e., the idea that things posses certain properties necessarily, that is, they cannot loose them without ceasing to exist (for example, Obama can't loose the property of being a human without ceasing to exist, that is - it is essential for him that he is a human).

    As to your questions: (a) and (b) don't necessarily overlap - according to Kripke there are some analytical truths that can be known only a posteriori (for example when we give definitions).

    (edit: on a second thought, this is a bit controversial perhaps, because Kripke doesn't say this explicitly, but it does seem to me to follow from other things which he does say - see below. Anyway, traditionally (and probably still) it was believed that if something is analytic then it is known a priori (but the converse is not true)).

    (a) does seem to entail (c), but perhaps Quine's "Two Dogmas of Empiricsm" could be seen as a challenge to this idea, since he claimed that no sentence is immune to revision, even "logical truths" (and he was also opposed to the notion of necessity).

    As I said, I don't know exactly what is meant by (f), but if my conjecture is correct (that it means metaphysical essence) then it is not the same as (e). It is true though, that if something is metaphysically essential, then it is metaphysically necessary, but it doesn't follow that all metaphysical necessity is
    concerned with metaphysical essence.

    (d) and (c) are not similar nor identical, because (c) is concerned with the formal/syntactical properties of, and relations between sentences, whereas (d) is about epistemology (that is knowledge). However it is widely believed that we know "logical truths" with absolute certainty.
  • Fafner
    And some general remarks about the relations between all these notions (you should keep in mind that this is philosophically very controversial topic).

    Traditionally philosophers thought that analytic/apriori/necessary and synthetic/aspoteriori/contingent always go together. But Kant famously argued that there could be synthetic a priori knowledge (like mathematics and geometry). And later, Kripke also argued that there could be necessary truths that could be known only a posteri (like that water is identical with H2O), and also contingent truths that can be known a priori (the standard meter in Paris is 1 meter long).

    There were also quite a lot of philosophers (and still there are some), especially the logical positivsts, that rejected the existence of a priori knowledge, and argued that all necessity is either logical or analytical.
  • numberjohnny5
    Thanks for taking the time to explain. I'll give what you've written some thought.
  • Srap Tasmaner
    Fafmer's summary is very good. These things can be confusing because philosophy addresses what is the case, how we know what is the case, and how we talk about what it is the case. You can sometimes reason from one of these to another, and then you have to be really careful.
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