continuing on with errol morris:
The actual quotation is from paragraph 241 of “Philosophical Investigations”:
“So you are saying that human agreement decides what is true and what is false?” –– It is what human beings say that is true and false; and they agree in the language they use. That is not agreement in opinions but in form of life.
This passage, as well as many others in “Philosophical Investigations,” has produced extended commentary. But Wittgenstein, notoriously difficult to pin-down, at least in this one instance, seems to be saying what he’s saying. And he opens the door (or the lid of Pandora’s Box) to a relativistic notion of truth.  In paragraph 241, it’s agreement between human beings that decides what is true or false. It suggests that we could agree that the earth is flat and that would make it so. So much for the relationship between science and the world. And yet, Kuhn made peace with this idea. He even made it the cornerstone of his philosophy of science. A couple of years later in “Structure,” Kuhn would write, “We may, to be more precise, have to relinquish the notion, implicit or explicit, that changes of paradigm bring scientists and those that learn from them, closer and closer to the truth.” 
ok understand that the attack on 'postmodernism,' on wittgenstein, kuhn etc, is just to boil it down to raw relativism and idealism and then shoot that fish. first off, i will not take that about 'postmodernism' in general, which is a huge grab-bag. but if you think you can just nail deleuze or foucault with this in a simple way, for example, you're wrong. and then the problem stretches way back: it's in hegel, in the pragmatists starting with peirce, and in some form virtually everywhere in modern philosophy. but second it is not without bite.
now one thing that always frustrated me about these figures (also quine, gadamer, davidson (brought in by morris on the other side), rorty etc) is that they just were not going to be nailed with this charge; they were always squirming out. so rorty (following davidson) always held that relativism was a senseless position that presupposed realism: if you couldn't compare your language to a world outside all languages, then you couldn't talk in terms of differing representational or conceptual schemes. wittgenstein was unpinnable on anything, and i always have had the feeling that was because he simply would not permit himself to be refuted, as that might reflect badly on his transcendent genius persona. well it's hard to refute someone who never really says anything clearly, or never actually resolves toward a flat assertion. morris says kuhn made his peace with relativism but he never did; he was constantly squirreling out of the charge through a million escape routes. in 1988, i thought it would be really refreshing to hear someone say: hell yes i'm a relativist, and then weather the storm, but then you couldn't do that and be a major philosopher. (at the time i was defining myself as a 'bone-head realist': i just went for an intractable world and a hard-ass truth you had to face up to.) and there are good reasons to be a relativist: the radically different interpretations of the world in different eras, culture etc have to make you wonder whether there is a simple standard or an objective reality they can be held up to, and it should make you worry about the objectivity of your own worldview: things like that have been used as instruments of oppression or to dismiss people and peoples. on the other hand there are very good reasons not to be a relativist too.
it's self-refuting, as someone, um, on morris's level, is going to point out relentlessly. isn't your own account of paradigm shifts 'merely' a paradigm? that all truth is relative to a culture, is that truth relative to a culture, etc? no one in their heart of hearts believes when pressed that any moral system is just as good as any other. and on and on. it's easy to attack, and that's one reason to make sure you can put someone neatly in the box: then you just stomp on the box.
so anyway, i've come to take the moves i used to regard as merely evasions a little more seriously. so wittgenstein does not at all say we can believe whatever we want and it will come true, or that agreement makes truth, despite what morris says he says. he's playing with the ambiguity of 'agreement': we share a form of life. we couldn't reach agreement on it - like sign a contract to believe it - because we can't see its edges; it's our world; it's not or it's not only a set of doctrines or beliefs. republicans share it with democrats, relativists with anti-relativists. 'form of life' is intentionally ambiguous, but it's intentionally rich too. nobody is really solicited as to their opinion on their own form of life, or can form such an opinion, and it could also encompass extra-linguistic physical objects and stuff (this is hinted at, for example, by wit's 'slab' language-game early on in the investigations). kuhn really had various complex ways of dealing with the concept of 'anomaly,' and what it is that forces a paradigm shift, and you'll notice that morris doesn't actually try to explain these globally different models of understanding as they have actually developed in the history of science. (i myself would strongly resist equating 'science' with objectivity, or framing the issue in terms of objectivity at all, or making science the sole center or deliverer of truth, and my own arguments for realism were more like 'drop a bowling ball on your foot and then try to believe that there are no real physical objects or that you are not yourself one such object,' etc. science is a style of representation, or many such styles.) the accounts of quine and davidson are remarkably, though perhaps deceptively, precise, and their ways around and through relativism are things you have to grapple with very elaborately or not at all.
as j.l. austin (who is a good figure to throw in here ) famously said, "there's the bit where you say it and there's the bit where you take it back." and these guys did that with relativism. but i've come to think that merely nailing these guys as relativists is actually simplistic. they're all different and none of them is that simple. irritating, but these are very hard issues! and morris i think ends up as a primitive; there are delightful excursions, but finally the charge is remarkably unsubtle, doesn't engage the real details of either science or the philosophies, and simply repeats the sort of simplistic complaint that people make when they don't want to grapple with the complexities, the sort of objection that people have made thousands of times. and he'll pick out the little bits of the texts he's attacking where that seems plausible. emergency! postmodernism! relativism! let's rally to truth, science, etc.: it's a very, a comfortingly rudimentary slam. but putting it mildly you need to read more carefully and, in general, work a lot harder.
but however there are real facts and a real world! (see i will never be a major philosopher because i do resolve into flat assertions.) and we are constantly in the midst of them. they're everywhere. human perception is a way that the world actually penetrates human bodies: we are it. we are not representational systems: we are part and parcel of a real, material world, individuated within it but not distinct from it. as we move through it, it moves through us. we are real things of necessity operating in and as part of a real environment: our senses constantly give us this real world. and so on.
one more thing i'll say: all the figures i've mentioned in this entry (well, other than morris) are dead. and now unlike '88 when these guys (foucault, deleuze, baudrillard, lacan, davidson, quine, rorty, the leering corpse of wittgenstein, kuhn, gadamer, derrida) were the eminent living (well foucault and lacan had died early in the 80s) dominant figures in philosophy, we now are beginning to look back on them as embodying an historical era (albeit complex). my feeling is that there is less at stake now in the question of whether kuhn is a relativist. the horizon has opened. we no longer have to destroy these people to make ourselves free or to get on to the next phase; we're in the next phase like it or not. their issues are not our issues, necessarily, and their ways of grappling with any issue are not our ways, necessarily.