What is it we intend that a theory should do for us? Is it meant to be a distillation of basic truth? Is it meant to be a fruitful guide to research. Is it meant to be a specific statement about the way things work?
It might be useful to distinguish between these different tasks, or between different kinds of theoretical formulation that serve them. One much discussed distinction is between highly abstract, general theory, and more specific, lower level theory. A famous sociologist of the mid-twentieth century, Robert K. Merton, favoured the latter, labelling it “middle range theory,” in contrast with the more abstract “grand theory.” How did he define, and why did he favour “middle range theory”? Middle range theory is specific enough to say what can or can not happen, and therefore can be tested by evidence. Grand theory is so abstract as to make it difficult to challenge with evidence.
Most “theory” in anthropology is highly abstract. I call it “heuristic theory,” because it is mainly meant to guide research by indicating what is important. Heuristic theory is more or less equivalent to grand theory, although sociologists, e.g Talcott Parsons and C. Wright Mills, tended to elaborate more than anthropologists do. Perhaps a paradigmatic example would be Clifford Geertz’s theoretical statements about religion, common sense, art, etc., which are frank in taking the form of definitions. Heuristic theory, and definitions, cannot be shown to be true or false; rather they are seen as either fruitful or not (or, "old" or "new," as fashion is our master, even in anthropology).
In contrast to heuristic theory are formulations that I would label “substantive theory,” which are more or less the same as Merton’s middle range theory. These tend to be fairly specific about something in particular, such that evidence can be brought to bear in support or in refutation. A simplistic example in one proposition would be “nomads do not have kings.” This substantive theory could be addressed by looking at as many cases of nomads as we can find, and seeing if any have kings. (My bet: don’t put your money on the kings.)
In addition to heuristic theory and substantive theory, there is epistemological theory, that asserts how we can know things, and may support or dismiss heuristic theory or substantive theory, or both. Usually epistemology is attended to by philosophers, but as nothing human is alien to anthropologists, we dabble in epistemology as well.