It is usually assumed that the `social construction' metaphor has one key meaning that is well understood across social studies of science. But a look at some of the texts that were, and are, central to introducing and defining `social construction' in science studies shows that there are widely varying uses of the metaphor: processes of construction differ with the types of objects that can be constructed. This paper identifies four prominent interpretations that have led to interesting insights and discussions. Though these different social constructions have generally been fused together in science studies, they are easily separable, and should be separated, since they are not equally tenable. In particular, `neo-Kantian' or `idealist' constructivism has weak arguments supporting it and, contrary to the standard rhetoric, is the least important of these different constructivisms to most of the actual work done in social studies of science.