Film Noir

Hitchcock's work is so unique that it can be called Noir or Horror or Thriller or Comedy or Romance or Tragedy and that can all describe the same film! Notorious has elements that are Noir and is often considered on the edge of Noir rather than straight-out, archetypal Noir. I would say that because its essence is "good" and the two main characters have a happy ending (of a sort) and that fate works for this couple rather than against them, it lies just outside of hard-edged Noir. The "fatal flaws" of these 2 characters do not lead them into real criminality (fighting Nazis seems to excuse just about anything in Hollywood) and by the story's end those flaws are being corrected. In real Noir, the characters have gone so far down the rabbit hole, that there is no redemption. (Compare to the ultimate noirs such as "Doulbe Indemnity" or "Criss Cross" for example.) The beauty of Noir is how flexible and universal it can be.

This is a very good question. I note that since you wrote it IMDB have included Noir in its description. I think it is Noir is style rather than content. The angles, the shadows. It does not fall into the Femme Fattal lures hapless man into situation that fate has decided can not end well. But a lot of the great Noirs don't follow the cookie cutter plots anyway, especially those where the male protagonist is a moral lawman.

There is however a darkness to the doomed romance, like many Hitchcock films the ending is ambiguous and left up to the imagination. Is Bergman poisoned beyond help?

It certainly has elements of noir. The feature that goes against calling it a film noir is that there is a reconciliation between the two principals. But it is steeped in noir.

And so is Suspicion, although I guess there the producers chickened out and balked at a dark conclusion inculpating Cary Grant.

For that matter, so is Vertigo, even though it is glorious, if not garish, color. Vertigo may be the culmination of film noir--a philosophical film noir tragedy of the highest order.

I see nothing noirish here. Ridiculous inflation of the term.