This is the second part of a short series comparing different theories of truth - please attend this meetup even if you didn't make it to the first part. We began by discussing the Correspondence Theory of truth, which characterizes truth as a relation between only two things: pictures of the world and the world itself. In this meetup we'll discuss theories that add more criteria into the scope of truth. This might including things like the way that we live, or the way that we would live if we were geniuses, or what makes most sense to believe.
The question is something like "Given that truth is more than just the agreement of picture and reality, what else is there?" While there are many answers to this question - and they're all up for discussion - I'd like to focus on two of them in particular: the coherentist and the pragmatist theories of truth.
Roughly, coherentism calls something true iff it is consistent with all or most of your beliefs. A judgement like "the cat is on the mat" might be true because it's consistent with "Jones says that the cat is on the mat" and "Jones never lies". The truth of the proposition is less plausible if you believe that "I do not see a cat on the mat", and also that "My vision is currently reliable". For a coherentist, truth exists in the way that all of your beliefs hang together, and there are no true beliefs in isolation.
There are many different versions of the pragmatist theory of truth but, very roughly, they all claim that truth is what works. Taken on it's face this seems absurd- suppose Jones steps over the mat because she believes a cat is on top of it, even though it's actually a small dog. We would want to say her belief was false, even though it worked out perfectly... Jones didn't trip on the dog. But pragmatists are actually saying something more subtle. Peirce, for instance, talks about what works only at the ideal limit of endless scientific investigation. For him, truth is what works for people who have collected as much evidence as possible (including, for instance, actually looking at the mat to see if there's a cat or dog on it). There's something compelling about this theory. Once we've collected all the evidence that we can we may as well believe whatever will satisfy our goals.
These theories manage to avoid one of the biggest problems faced by the Correspondence theory, which is famously unclear on how we could possibly know whether something is true. While Correspondence compares a picture only to the world itself, both Coherence and Pragmatism bring much more to the problem including evidence that we actually have access to. Obviously something is gained by this, but much seems to be lost. When we talk about truth, when we pine for it or insist on something's being true even in the face of compelling evidence to the contrary, we're imagining truth as something permanent. The word 'holy' comes to mind. Could truth really be something so fickle as to depend on what I currently believe? Honestly, nobody says this better than Rorty in this very short video (with bonus dutch subtitles) - http://www.youtube.com/watch?v=CzynRPP9XkY
So (http://www.youtube.com/watch?v=CzynRPP9XkYSo) come join us for a discussion about what comprises truth. No prior reading is required, but if you'd like to prepare you're encouraged to look into William James or simply google "coherentist theory or truth". I'm certain that Bayesian Inference will come up, and it might be worth looking into it ahead of time. Or just spare a thought for the concept of truth in general. When you use the word, what do you really mean? What are you willing to count as true (as opposed to a mere belief or opinion)?