Looking at drives

A little reflection on drives and their sources and aims--I am highly questionable about my reading of what Strachey is saying, because I don't have the German on me right now. But I'll see what is going on and return to this. In the meantime...

Although drives are wholly determined by their origin in a somatic source, in mental life we know them only by their aims.
-All quotes from "Instincts and Their Vicissitudes," SE 14:121-22: throughout I've rendered "instinct" as "drive".

What Freud means here is that though drives are determined by that somatic process whose being stimulated is represented by the instinct (their source), in mental life itself we know them only by their attempt (within mental life) to remove that stimulation of the somatic process--what Freud calls the "aim" of the drive. (This is the reason why later Freud will say that drives are also only present to the unconscious--just as much as consciousness--through their "representatives.")
To put it a different way, though drives get their character (roughly, "what distinguishes one from another," as Freud goes on to say) from the sort of stimulation which they represent, they can't be seen in mental life except in terms of how they try to rid themselves of this character. We can't look at a drive then and see how the character was formed. We can only postulate that it was formed from looking at how it proceeds to try and get rid of this form--that is, how it uses this form. Thus Freud's next sentence:

An exact knowledge of the sources of a drive is not invariably necessary for purposes of psychological investigation; sometimes its source may be inferred from its aim.

In short, from all this we understand a sentence that puzzles Strachey and which he very confusedly translates--thus making it possible for others to make the same error. We understand that what distinguishes a drive from another drive is its source, but we cannot and really need not know the source to also perceive this difference. The difference--i.e. the source--appears later in the particular aim of the drive--as we said, in its twists and turns (primarily, its picking up of what Freud calls "objects"--things that help the aim) made so that it can divest itself of the stimulus that formed it. That is, Freud means what he says here:

What distinguishes from one another the mental effects produced by the various drives may be traced to the difference in their sources.

Which means effectively that we aren't distinguishing between drives when we see different ones, but rather between aims--thus what is the object of this sentence is "the mental effects produced by the various drives," not the drives themselves. The mental effects are all we can get at--and when we talk as if we are distinguishing drives, we are really talking about what happens or appears later, what emerges from the drive. To sum this all up, Freud adds the sentence that Strachey translates as the following:

In any event, it is only in a later connection that we shall be able to make plain what the problem of the quality of drives signifies.

Now, if I'm not mistaken, what this sentence really means is that only later--as we witness the aim--is it clear what the difference (in quality) between drives is. But Strachey takes this sentence to mean, I think, that later on in some future paper Freud will elaborate the problematic question of the differences between drives. Thus he says, in a footnote to this sentence, "It is not clear what later connection Freud had in mind." I think it should be rendered the following way:

In any event, it is only in a later event that we shall be able to make plain the the problem of the meaning that qualities of drives have.

In other words, it is only when we see the aim that we will be able to make plain the problem of the quality of drives: the problem being what differentiates them in their character, what their particular meanings are that make them different from each other.