First, let us stipulate that an identity is a feature of consciousness, an aspect of mentality. And let us stipulate further that an identity comes to one as a result of one's experiences in the world, and one's attempt to make sense of those experiences. These assumptions are not indisputable -- it might be maintained that one can be unaware of one's social identity, or that one's social identity is constituted by one's position in society (a structural fact rather than a fact about one's experience). But these are credible beginnings.
Next, it is clear that an identity is not one unified element of consciousness--an ineffable but uniform sense of being "Irish," "Southern", or "Hindu". Instead, an identity must be more like a flavor or a scent: a complex but distinctive blend of more basic elements (tastes or smells). This feature already implies several broad forms of differentiation across an identity group: the mix of elements may be different (a little rosemary blended into the scent of a rose), and there may be differences in the intensities of various elements in the mix.
What are the components of which an identity is composed? Here are some plausible candidates: memories and stories, values, emotions, ways of reasoning, factual beliefs, a sense of justice. (Notice that some of these are content and some are mental process--beliefs versus reasoning, for example). Presumably there are other components that should be considered; but these will do for now.
Where do these elements come from for the individual? Through learning and lived experience. One's rich and intimate experience of living with others -- family, friends, neighbors -- who possess values and who tell stories about "who we are" is a thick form of personal development. And one's own experience of the values and emotions of others -- the experience of racism and discrimination if one is black and gay -- is a powerful catalyst for shaping one's view of the world. This experience shapes one's values, sense of justice, and key memories.
Now return to the question of variation across a group. It is clear that an identity shaped along these lines will show great variation across individuals. Each individual's experiences are somewhat different. And each person will process those experiences somewhat differently. What makes an identity a socially shared identity is the fact that some groups have a high degree of commonality of experience -- both through exposure to the prior generation and through one's own experiences in everyday life. But at the same time it is apparent that there will be substantial variation in values, memories, narratives, and styles of thought within the identity group. So the social identity of being "Latino", "Polish", or "disabled" should not be expected to be a uniform and homogeneous feature of consciousness. The metaphors of "flavor" and "patchwork" serve us better.
This brings us to a preliminary conclusion: social identities should be expected to show significant variation across individuals.
[It is intriguing to note that it would be possible to pursue this theory of the psychological constitution of a social identity by trying to measure and map the variations of the components across a population. Opinion surveys would permit measurement of the distribution of certain diagnostic values and judgments of injustice, for example. We could then ask questions like these: Are these characteristics correlated within the population? Do some variables show more variance than others? How do these distributions of the variables compare with those of the general population?](See Mentalités, Identities, and Practices for more on this subject.)