I received a tertiary education in Physics and learnt about finance and accounting the hard way. As such, postmodernist philosophy is pretty much alien territory to me, though not for long, once I haul my raggedy ass through Russell's History of Western Philosophy*.
Anyway, I picked up and read Ayer's Language, Truth and Logic, under the foolish assumption that, being such a slim volume, I should be able to get through it quickly. 2 months later, I've finally finished reading it (though I've yet to polish off the appendix) and have decided to summarise my understanding of it here, in the hope that somebody with the m4d skillzorz to comment can indeed do so and maybe tell me if I'm missing something. So, here's the long story short...
Ayer's book champions the cause of logical empiricism, and so all human knowledge can be broadly divided into 3 types:
1) A priori truth. This comprises axioms that are, by definition, true, and the theorems that we derive from them. The only fields of human knowledge and inquiry that has ever offered this kind of truth consistently is maths and logic.
2) Empirical truth. i.e. Propositions that can be verified empirically. This is the foundation of science as we know it and all of the theorems and propositions we arrive at are assumed to have the qualifier "until proven wrong". For instance, the Theory of Evolution is an empirical truth and nothing has yet been observed to prove it wrong. The good scientist will accept this as true but must always keep his mind open to evidence against it. The criterion of how one verifies an empirical truth is codified in the verification principle, which is a bit heavy, so here's a link to the Wiki.
3) Anything which is neither an a priori truth nor verifiable empirically is in the realm of bullshit**. But it is important to realise that, limited creatures that we are, bullshit is in fact a necessary part of life. For example, we speak glibly of 'good' and 'evil' to get people to behave***, or we use bullshit as a sort of scaffolding with which we build our understanding of the universe. Like anything else, bullshit can be used for good or ill, but it's vitally important that we recognise it for what it is, that is, we remember to strip off the scaffolding when it becomes unnecessary.
Metaphysics, that is, "the branch of philosophy investigating principles of reality transcending those of any particular science" as stated by Wikipedia, offers neither a priori nor empirical truths. As such, metaphysics is useless bullshit. This conclusion drew much ire from philosophers who staked pretty much their whole careers on metaphysics.
The Truth - No such thing. Truth is a property of a proposition. i.e. A proposition can be true or false. Looking for the Great Truth of Life, the Universe and Everything is in the realm of metaphysics, and therefore useless bullshit.
The existence of God - Since most definitions of God fail to be either a priori or empirical, God is quite likely bullshit. Moderates and fundies alike seem to favour a definition of God that involves Him being outside our universe and therefore unobservable, so empirical verification is out. Hence any statement either denying or affirming his existence is useless bullshit. From this we can imply (though it's not stated in Ayer's book, coz he'd have been lynched) that all religion is in fact bullshit of the most meaningless and unnecessary kind.
The book goes on to use this framework of logical empiricism to scrutinize some of the major philosophical conflicts of the day, e.g. Rationalism vs Empiricism, Realism vs Idealism and Monism vs Pluralism. Seeing as the conflicts all occur on metaphysical fronts, it's quickly revealed that there is no conflict, and that said conflicts were in fact grounded in, you guessed it, useless bullshit.
I've decided I like Alfred Ayer. What he says is very much in concordance with my own outlook on Life, the Universe and Everything, and with my conclusions from my readings of Zen and the works of Bertrand Russell. A truly remarkable book, when you consider the fact that Ayer wrote it at the age of 23.
Comments particularly welcome for this post. Just don't come here with useless bullshit ;-)
* Which I thoroughly recommend to any student of world history, though only as a complement, not an alternative.
** Actually, the word he uses is 'nonsensical', but 'bullshit' has the right kind of umph to it, yes?
*** Or in some cases, to get people to do what you want.