I make my points concrete by developing a taxonomy of theories of mental content, but the main points of the paper concern not merely how to classify, but how to understand, the theories. Also, though the paper takes theories of mental content as a case study, much of the discussion is applicable to theories of other phenomena.

To a first approximation, the difference between the traditional and the proposed taxonomies turns on whether we classify theories of content by, on the one hand, their implications for a non-redundant supervenience base for content facts (i.e., for facts about what contents thoughts have) or, on the other, by their constitutive accounts of content. By a “constitutive account,” I mean the kind of elucidation of the nature of a phenomenon that theorists have tried to give for, for example, knowledge, justice, personal identity, consciousness, convention, heat, and limit.

The tendency to taxonomize by supervenience base is encouraged, I suggest, by a failure to keep clearly in view a distinction between constitutive and modal determination. Many philosophers would accept that a constitutive account cannot be captured in purely modal terms. Giving a constitutive account is not the same as specifying modally necessary and sufficient conditions. Nevertheless, philosophers often try to cash constitutive claims in modal terms. A case in point is that theories of content tend to be conceptualized in terms of the theories’ implications for a supervenience base for content facts.

My thesis goes beyond the by-now somewhat familiar proposition that not all modal determinants of a phenomenon are constitutive determinants. One who has taken that point on board might nevertheless conceive of a philosophical account as an attempt to specify constitutive determinants of the target phenomenon that make up a non-redundant supervenience base for the phenomenon. Shoehorning a philosophical account into this form leaves out elements that are modally redundant, but may be explanatorily or ontologically significant. For example, when a constitutive account has multiple levels, the different levels will typically be modally redundant. Formulating the account as a specification of a supervenience base of constitutive determinants will therefore flatten the account into a single level.

Many of my arguments can be illustrated by considering the place of normativity in the theory of content. The new taxonomy gives a distinct niche to <i>normative theories of content</i> – theories that explain a thought’s having a certain content at least in part in terms of the obtaining of normative facts. By contrast, on a traditional map, normative theories are invisible as such because normative facts supervene on non-normative ones.