Here is an odd question the oddness of which is inaudible if you've had the 'right' kind of philosophical education: 'What is it you grasp when you grasp the meaning of what someone is saying, when you grasp the significance of their gestures, the intention in their utterance, the feelings they express?'
And here are two kinds of answers that might present themselves once we've both a) habituated ourselves to the oddness and b) unwittingly subscribed to a somewhat alienated conception of meaningful behaviour and its appreciation, in such a way that we don't take the question to answer itself and have done with it.
i. What you grasp are the rational relations between the action/gesture/thought/emotional reaction and other thoughts, intentions, feelings, actions, beliefs etc. of the person.
ii. What you grasp are the causal sources in the mind of the behaving subject - their intentions etc. - that give rise to their actions and utterances.
If you are feeling like hedging your bets you could always be a hybrid theorist. 'Oh, understanding intentional action involves placing an agent's actions in relation to both the reasons that rationalise it, and also the motivations or intentions or various dispositions that cause it. Perhaps unlike anything else in the natural or social world which at first we intuitively imagine to have a singular logical character, our understandings of action - when I with apparent unity and simplicity just get the univocal what of what you're doing or what you're on about - actually draw on two distinct (rationalising, causalistic) canons at the same time.' Well, fancy that.
Now, I suspect that a good deal of the literature in the philosophy of action springs up as an intuitive reaction to the two above positions, and is an attempt to spell out these feelings in prose. (It doesn't present itself this way, but, but...) In this post I want to urge the logical univocity of our understanding of one another in our active lives, to suggest that this form of intelligibility and its object are sui generic, and to propose (following Heidegger I guess) that the basic character of this interpersonal grasp and of what is thereby grasped is just so basic, so much a part of or right under our noses, that we struggle to even bring it into view. With the result that we bring into view only its dependents and then try to win them back their heritage through rather unconvincing appeals to alleged stigmata of their bloodline.
i. As regards the rational relations pundit, we might start to feel her offerings as a little thin, too horizontal, too logical, with not enough animal oomph, insufficiently agentially alive. For when I grasp just what you are doing or getting at, I don't typically undynamically, statically, see it as reasonable in the light of such and such thoughts etc that you happen to have. (It's not a safe inference from a) something might not be safely thought intelligible if one could not also reconstructively track certain rational relations between it and this or that other intentional attitude, to b) this tracking is how we understand it. For might it not rather be that what makes for the possibility of rational reconstruction is also what makes for the possibility of understanding - 'effects of a common cause', so to speak...? So that I can give the reasons for your action because I understand it - not that I can understand it because I can give the reasons for it.) Rather I relate to it as a piece of active self-becoming, as an enactive aspect of the self-unfolding of who you are. 'There he goes, off to the bar again, holding the barmaid's attention with his characteristic twinkly eye, his self-deprecating yet assertive comportment...' I'm not sitting there rationally reconstructing Jeff's behaviour: 'Er, Jeff wants some beer, he believes that there is beer at the bar, that the barmaid can be pressed on to serve it, that if he hands over some of the lumps of metal and pieces of paper in his pocket they will give the beer to him, that it goes in a vessel rather than being poured straight into his throat from the tap, that...' All of that is true, sure. But isn't it rather that the intrinsic intelligibility of some stretch of Jeff's behaviour is what makes it apt for its rational hanging-together-ness with other of his actions and feelings and intentions and thoughts or, if that is going too non-holistic, that at the least it is not simply in its lateral rational relations that its intelligibility consists? I get the stretch of behaviour, and I get how it hangs together with this or that else that you think or feel, and it's the getting that we're interested in here. Getting at juncture Y does not explicate getability at juncture X: the phenomenon of getability - which getability is what we're here trying to get at - has just been presupposed.
(Note for initiates: This is not me repeating Davidson's allegedly successful argument against 'rationalists' - that reasons by themselves are not enough and so we need to supplement them with causal glue. You know the story: someone might have several beliefs or wishes which would rationally explain their action, but yet only properly be said to act for one of them. Julia Tanney utterly disposed of that argument some time ago, when she pointed out that we can only understand why some of the reasons might not be active if we specify defeating conditions on those. We don't need causal glue; instead we need rational solvent. It is however articulating what I believe to be a decent disquiet which might have got mis-expressed by Davidson in the wrong kind of rational reconstruction.)
ii. As regards the causal relations theorist, well, we may at least feel now that the phenomenon - the behaviour under its aspect of getability - is at least incarnate, so that there is the possibility of pulsion on the horizon. But then other worries crop up: we notice how rather too close we are to something which feels brute, uncomprehending (the kind of sense we make of why the bridge collapsed is just not the kind of sense we make of one another) - and to a mode of explanation which is paradigmatically explicated with examples of merely externally related relata (i.e. where cause and effect do not constitute one another) - and to a mode of explanation which everyday we precisely pit against the agential (i.e. when we have to do with undergoings as opposed to undertakings, happenings as opposed to doings - when we think about interferences in agency, for example, when we think about ourselves under the aspect of patient rather than agent). Thus Davidson introduced causation to glue active reasons to actions - but then leaves us with the problem of wayward causal chains when thoughts or feelings which don't constitute reasons nevertheless accidentally propel behaviour.
So, so: what then? What do we have to do with when we grasp intelligible action and utterance? What is the mode of comprehension and what is its object?
What I want to suggest here is that it would simply be disastrous to try to find some other scheme to accommodate humane sense making - a scheme such as the logical space of reasons or of causes. Rather than try to fathom it - getability - by placing it here or there, instead we would do better to simply offer it acknowledgment, remind ourselves of it in its sui generic being. What we have to do with, again, is the matter of understanding what someone is doing or saying. If we are not already sunk down in the arena of together-grasping, of com-prehension, of standing alongside, under-standing, then we may as Jaspers says need to sink ourselves down empathically with one another. This autonomous mode in which we are disclosed to one another, in our being-there for others, in their being-there for us: we know perfectly well what it is, really. The problem however is that this form of intelligibility and this mode of comprehension - a mode which is of a piece with our perceptual encounters themselves - are just so basic that we tend to overlook - and then tacitly presuppose - them. Sheer 'presence' and 'being-there' are so under, or of a piece with, our noses that they are utterly overlooked by the theorist.
And, and, it really is no more mysterious for all of its sui generisity - after all, not everything can be explained in terms of something else, and those things which can't (e.g. temporal and spatial properties) aren't obviously any more mysterious because of their recalcitrance to reduction.