Jean-Paul Sartre, answered from the texts and cited to the page.
Anguish is not a mood, not a psychological trembling before some threatening object. It is the structure of freedom becoming conscious of itself. Consider what happens when I stand before a temptation — wine I should not drink, a resolution I made yesterday, a gambling table I swore to avoid. The past resolution exists; it was real. But it exerts no force on my present consciousness, because my free present-to-come nihilates it, puts it out of circulation the way spent currency is put out of circulation.1
Nothing — literally nothing — prevents me from drinking, from playing, from breaking the resolution. And it is before that particular nothing that anguish arises: the nothingness of my past's power to act on my present.2 This is why the common phrase "I don't trust myself" is so philosophically precise: it is anguish at nothing, since nothing allows me to foresee what I shall do, and even if I could foresee it, nothing could prevent me from doing it.3
The objection arrives quickly: surely this is merely ignorance of the psychological determinism that underlies my acts, the unconscious motives lurking in the depths. But this misses the point entirely. Even granting such determinism, anguish would then be a consciousness of not knowing its true causes — and in that case I would appear to myself as a thing in the world, my own transcendent situation, and what I experienced would dissolve into fear, not anguish.
Fear is the synthetic apprehension of something transcendent as threatening; anguish is what remains when the threatening thing is not transcendent at all, but is the nothing that insinuates itself between my motives and my act.4 My motives do not cause my act. They encourage, they incline, they press — but between the motive and the act there is always a hiatus, a missing link, and it is the absence of this link that deprives me of any excuse.5
A motive is never in consciousness; it is only for consciousness.6 This is why anguish is the experience of responsibility at its most naked. I have no recourse to any value set against the fact that it is I who maintain values in being; nothing can insure me against myself, cut off from the world and from my essence by this nothingness that I am.7
I decide alone, without justification or excuse. Anguish is freedom's reflective self-apprehension — it arises the moment I disengage from the world in which I was committed and apprehend myself as a consciousness that has a prejudicative sense of its own possibles.8 It is opposed to what I call the spirit of seriousness, which grasps values as if they came from the world itself, as if the meaning my freedom gave to things were inscribed in things rather than projected by me onto them.9
There is one further movement worth tracing. Anguish before a possible one does not want to realize is anguish at the nothingness separating oneself from that possible — the fact that Nothing prevents its realization. And this anguish tends to suppress itself by realizing the possible: the transgression provisionally causes anguish to disappear, replacing the nothing with a plenary facticity.10
But notice that this suppression is itself a choice. Nothing obliges the act any more than nothing prevents it. The nothingness is double: it separates me from the forbidden possible, and it separates my motives from whatever possible I do pursue. Both nothingnesses are given in anguish simultaneously. So: the existential grasping of our facticity — the sheer brute thereness of existing at all — is Nausea.
The existential apprehension of our freedom is Anguish.11 The two are not symptoms. They are the fundamental tonalities in which human reality encounters what it is.
future freedom is negation of present freedom. I cannot commit myself, because the future of freedom is nothingness... my present-become-past will be nihilated and put out of action by my free present-to-come.War Diaries, pp. 148–149
It was before that particular nothing I was so anguished: that nothingness of my past's means of acting on my present. Nothing to be done.War Diaries, pp. 148–149
the common phrase 'I don't trust myself' [j'ai peur de moi] is precisely an anguish at nothing, since nothing allows me to foresee what I shall do and, even if I were able to foresee it, nothing could prevent me from doing it.War Diaries, pp. 148–149
the synthetic apprehension of something transcendent as fearful is fear. We can characterize this freedom, disclosed to us in anguish, in terms of the existence of this nothing that insinuates itself between my motives and my act.Being and Nothingness, pp. 127–128
the motives which might encourage one to realize a possible are always separated from this possible by a hiatus of nothingness... it's the absence of this link that deprives us of any excuse.War Diaries, p. 149
a motive can only appear as a motive as the correlative of one's consciousness of that motive... a motive is never in consciousness: it is only for consciousness.Being and Nothingness, pp. 127–128
I have no recourse, and I cannot have recourse, to any value to set against the fact that it is I who maintain values in being; nothing can insure me against myself, cut off from the world and from my essence by this nothingness that I am. I have to actualize the meaning of the world and of my essence: I decide it alone, without any justification or excuse.Being and Nothingness, p. 134
Anguish is therefore freedom's reflective self-apprehension... it arises out of the negation of the calls made upon me by the world; it appears as soon as I disengage from the world in which I was committed, to apprehend myself as a consciousness with a preontological understanding of its essence, and a prejudicative sense of its possibles.Being and Nothingness, p. 134
it is opposed to the spirit of seriousness, which grasps values on the basis of the world and reassures us by conferring a reifying substance on values... grasping the meaning my freedom has given to the world as if it came from the world.Being and Nothingness, p. 134
Anguish at a possible one doesn't want to realize is, in fact, anguish at the Nothingness which separates one from that possible... the transgression provisionally causes anguish to disappear, by replacing the Nothing with plenary facticity.War Diaries, p. 149
Thus the existential grasping of our facticity is Nausea, and the existential apprehension of our freedom is Anguish.War Diaries, p. 149