Is there a valid (i.e., non-historical) reason why personality psychology and social psychology are so often lumped together as one branch of psychology? There are PSP journals, PSP conferences, PSP brownbags… the list goes on. It all seems kind of odd considering that, in some ways, personality psychologists and social psychologists have completely opposite focuses (foci?). Personality psychologists are all about the consistencies in people’s behavior, and classify situational variables under “measurement error”; social psychologists care not one whit for traits, and are all about how behavior is influenced by the situation. Also, aside from the conceptual tension, I’ve often gotten the sense that personality psychologists and social psychologists often just don’t like each other very much. Which I guess would make sense if you think these are two relatively distinct branches of psychology that, for whatever reason, have been lumped together inextricably for several decades. It’s kind of like being randomly assigned a roommate in college, except that you have to live with that roommate for the rest of your life.
I’m not saying there aren’t ways in which the two disciplines overlap. There are plenty of similarities; for example, they both tend to heavily feature self-report, and both often involve the study of social behavior. But that’s not really a good enough reason to lump them together. You can take almost any two branches of psychology and find a healthy intersection. For example, the interface between social psychology and cognitive psychology is one of the hottest areas of research in psychology at the moment. There’s a journal called Social Cognition–which, not coincidentally, is published by the International Social Cognition Network. Lots of people are interested in applying cognitive psychology models to social psychological issues. But you’d probably be taking bullets from both sides of the hallway if you ever suggested that your department should combine their social psychology and cognitive psychology brown bag series. Sure, there’s an overlap, but there’s also far more content that’s unique to each discipline.
The same is true for personality psychology and social psychology, I’d argue. Many (most?) personality psychologists aren’t intrinsically interested in social aspects of personality (at least, no more so than in other, non-social aspects), and many social psychologists couldn’t give a rat’s ass about the individual differences that make each of us a unique and special flower. And yet there we sit, week after week, all together in the same seminar room, as one half of the audience experiences rapture at the speaker’s words, and the other half wishes they could be slicing blades of grass off their lawn with dental floss. What gives?
Personality psychology and social psychology share the (focus on the) concept of “self” – the former studies the impact of the self on cognition/behaviour, the latter, other selves on cognition/behaviour, although increasingly the distinction is seen as arbitrary; social psychology’s typical definition of “how cognition/behaviour is influenced by the actual, implied, or imagined presence of others” actually becomes personality psychology merely by considering that one conscious self-image is often intuitively considered as “other” (as in cognitive dissonance, whereby ones actions contradict ones self-image).
This is an interesting question and I’m not sure if there is a clear answer. One of the historical curiosities about the two fields is that Gordon Allport is often considered the father of personality psychology, and he had a brother Floyd who was influential in social psychology. In my whimsical moments I wonder if the “sibling rivalry” between the two fields began with these two brothers.
There was for a number of decades a heated “person-situation debate” about the respective contributions of personal traits versus situational variables to a person’s behaviour. Interestingly before this debate ignited Kurt Lewin had argued that behaviour is a function of both the person and their environment. Perhaps they were lumped together based on Lewin’s theory that personal and situational variables are two components of an interacting “field” and therefore these components need to be understood in respect of each other. But as you say, there are lots of focal areas of psychology that overlap and they are not all lumped together apart from belonging under the umbrella of psychology. I suspect that they are lumped together today mainly because of their historical theoretical association and perhaps because they are both seen as especially “soft” areas of psychology.
I think Stormy does make a valid point that they both consider the “self” but from different angles, so social psych does include a theory of “personality” albeit one that de-emphasises individual differences.