I understand that old d.T. is far more read in America than here in Europe. - Maybe some of the Americans can help me with this?
I'm certain that he's an TP. His writing style is informative as opposed to directive. His interests drift towards political and historical contingencies rather than people or the present. - And contemporaries, both American and European, noted his lack of warmth and his preference for being impersonal.
His momentary urges for solitude are also well-documented, which could seem to indicate Introversion, though this does not have to be the case, as he was also suffering from melancholic episodes (depression not having recieved its name yet).
I would have a hard time going with S as the man was strongly future-oriented as well as possiblity-oriented (studied America to see what could be applied in France). So I'm left with INTP or ENTP.
He might well be eigter, though the argument could be made that his reasoning unconciously seems to revolve around extroverted matters such as geographical, political, and historical matters rather than around purely philosophical concepts i.e. his overall describtion is chaotic and fractured rather than top-down conceptual.
Furthermore, he is very fond of making comparisons (A in America is like B in France with variation Y) and drawing parallels, which again seems to point to an Ne primacy.
Also, while black spells can certainly hit anybody, it's kind of a stable of the ENTP-with-an-overly-philosophical-bent subtype.