Originally posted by Dartmoor Dave I think that's a really interesting and thought provoking point. Can a photo ever really capture a personality, or does it only ever capture a person's apparent state of mind at a particular moment? I don't know the answer, but I'm going to enjoy pondering it.
At one level, it's true that a single image captures a single moment which thus captures a single state of mind. And yet a single state of mind can be an amalgam of feelings that modulate the person's expression, eyes, posture, etc. in different ways (e.g., a smiling face with sad eyes on an erect, commanding body posture). The result is a multidimensional glimpse of the personality.
The foreground/background environment can significantly add to the portrait. People (and their portrait photographers) can select and curate their surroundings -- a messy workshop, a wall of accolades, a tidy garden, a humble cabin in the woods. These surroundings convey other states of mind integrated over a lifetime and that adds depth to the portrait and give hints about the personality behind the eyes. (In otehr cases, the surroundings might be incidental.)
Aperture is the dial that controls the relative contributions of the face versus the surroundings to the image. Sometimes it is nice to be able to read the titles on the spines of the books behind the person to show who they are and what they think about. Sometimes it's better just to have a blurred-out bookshelf.
It is interesting to think how much of a person's personality can be crammed into a single image. It's also interesting to consider that maybe the blur of f/1.4 creates ambiguity to more strongly state that there are hidden depths beyond the single state of mind and single moment of that photograph.