On what basis do we derive logic? [duplicate]

Question

I find that using logic is purely pragmatic.We use many forms of logic to conclude various things about our "world" which is through epistemology.But yet, the fallacy I find here is that we assume that the information we conclude is true. After all, if I am not sure about my existence, then how can I be sure that my experiences are real?For all I know, I might as well be a cat or even “nothing”.If this is the case; when is the point through all this superficiality do we come up with the principle of logic?

Answer 1

First, we must define logic. Generally, logic is a formal system to determine truth. You've jumped ahead of the problem by asking if you exist, you don't even know you can verify anything. Let's grant that you're real, it's still possible that's there's no conceivable way that you could verify that. You must assert some axiom(s), from which you can derive rules for your formal system. The (often unwritten) first of these axioms is usually that you experience things, so there either is or is not a cause for those experiences.

The first sentence you wrote reminded me of Dharmakirti's two uses of the word "reality." In his conception of Buddhism (you can google Buddhist logico-epistemology) there is a conventional reality, in which you 'know' you experience the world, the objects and people in it, etc. However, the ultimate reality is that of emptiness/non-existence. The reason is, the inference from seeing other people's actions to them actually existing only has one example case: that of ourselves. The ultimate ethical implication is that you can still lead a compassionate and fruitful life even if the world 'isn't really there.'

Of course, there are many logical systems that affirm the existence of a real, external world that some of the most brilliant scholars in the world subscribe to. Phenomenologists like Heidegger would argue that you have a pre-logical access to ontology. That is, you are. You don't have to 'know' this in any exceeding way.

You may be interested in reading about Phenomenology, Nagel's works on consciousness, and maybe stuff like 'embedded consciousness' and Daoism.

Answer 2

René Descartes' deus deceptor maximus was posited to be capable of tampering with logic itself. One could ask then, is 2 + 2 (really) = 4?!?! That's what I would call radical skepticism.

Where does logic come from? Frankly, I haven't come across a work that delves in any detail the origins of logic. The basic idea is quite simple if you give it but a moment's reflection - how the truth/falsity of propositions implies the truth/falsity of other propositions (inferential link). So I suppose, given this is our primary concern, logic sprang from a desire/need for truth. Logic, as is obvious now, allows us to construct a weltanschauung of true beliefs that a) help us in understanding reality and thereby b) participating (living) in reality well.

That said, some logicians have treated logic as toy and tinkered around with some of its laws/rules e.g. the law of noncontradiction is done away with in paraconsistent logic and dialetheism. This, if memory serves, was inspired by Bolyai's and Lobachevsky's work in non-Euclidean geometry.

So, is logic a tool or is it a toy, both, neither?

Answer 3

Aren't you just assuming that there are assumptions? There is a problem in metaepistemology where the usefulness of the concept/word "knowledge" is called into question. Some analysts think that the concept of knowledge is irreducible, like a concept of a specific shade of color say, while many have historically held that the concept can be broken into definitional pieces (the classic, "refuted" example being "justified true belief").

But so logic, as the art or science of derivations, is then either self-derivative in some obscure manner, or is not derived from anything. You question your existence, but you don't seem to have doubts about the meaningfulness of your question itself. If "knowledge" is just another word that we can use or not at our leisure (for contextualist reasons, perhaps), then we are free to say that we don't know anything, indeed that no one "really knows" anything, without this having any important consequences whatsoever. Well-established scientific theories will remain closer to the truth than superstitious dogmas of yore, mathematicians will still be able to prove various complex theorems (and recognize when they are able to do so), logicians will be able to explain how various inferences work, and all will be well with the epistemic world.

All that would be lost is the word "knowledge," then. How much of a loss is that, really? Abelard is talking with Eloise, he looks up at the sky and says, "Look! The moon is turning into green cheese!" Eloise, who is not a fool at all, is not prompted to ask Abelard how he "knows" this. She bypasses that and just asks, "Are you sure your eyes are working properly?" Abelard realizes that there's some gunk on his bifocals, and in the moonlight at some random angle, this has distorted his sight. What good, or what difference, does it make to use the word "knowledge" in relation to any of this?

In other words, contra G. E. Moore, there need not be anything wrong with saying, "2 + 2 = 4, but I don't believe that it does." More pointedly, there need not be anything wrong with saying, "When I add 2 and 2, I get 4; but I don't know that 2 + 2 = 4, even when I perform the addition and get 4." There is no room for skepticism, here, because skepticism presupposes that the question, "Do I know that [insert some possible fact]?" is really significant in the first place.