Categories of phlosophy

2.1 The Uses of Category Distinctions

Those who focus on articulating category distinctions rather than on laying out complete systems of categories generally invoke categories not in hopes of providing answers to such basic metaphysical questions as ‘what exists’, but rather as a way of exposing, avoiding, or dissolving various presumed philosophical mistakes, confusions, and paradoxes.

Thus, e.g., Russell and Whitehead introduced type theory (which might in some sense be considered a theory of categories) to avoid a certain form of paradox found in Fregean set theory (where we must consider the putative set of all non-self membered sets, which is a member of itself if and only if it is not a member of itself), liar’s paradoxes (“This sentence is false”, which is true if and only if it is false), etc. On their analysis, paradoxes like these arise from the attempt to form an illegitimate totality by trying to collect into a single totality a collection that has members that presuppose the existence of the totality. To avoid such paradoxes, we must accept that “Whatever involves all of a collection must not be one of the collection” (1913/1962, 37) and thus that such totalities (involving all of a collection) must be of a higher type, making, e.g., classes of sets of a higher type than are sets of individuals, and so on, leading to an infinite hierarchy of types. The type-mixing paradox-generating claims are rejected as ill-formed and meaningless (1913/1962).

Most famously, Ryle (1949) introduced the idea of the category mistake as a way of dispelling the confusions he thought to be rampant in the Cartesian theory of the mind, and thus of dissolving many apparent problems in philosophy of mind. According to Ryle, one makes a category mistake when one mistakes the logical type or category of a certain expression (1949, 16–17). Thus, e.g., a foreigner would make a category mistake if he observed the various colleges, libraries, and administrative offices of Oxford, and then asked to be shown the university. The foreigner mistakes the university for another institution like those he has seen, when in fact it is something of another category altogether: “the way in which all that he has already seen is organized” (1949, 16). The category mistake behind the Cartesian theory of mind, on Ryle's view, is based in representing mental concepts such as believing, knowing, aspiring, or detesting as acts or processes (and concluding they must be covert, unobservable acts or processes), when the concepts of believing, knowing, and the like are actually dispositional (1949, 33). Properly noting category distinctions may help alleviate a variety of philosophical problems and perplexities, and the idea of the category mistake was widely wielded (by Ryle and others) with this aim.

Another potential application of work on categories lies in the idea that various mistakes and puzzlements in ontology can be traced to the mistaken belief that category-neutral existential and quantificational claims are truth-evaluable (see Thomasson 2007). A great many arguments in ontology rely on claims about whether, in various situations, there is some object present (or how many objects there are), where the term 'object' must be used in a category-neutral way for the argument to go through (Thomasson 2007, 112–118). But if truth-evaluable existential and quantificational claims must tacitly presuppose some category or categories of entity over which we are quantifying, then such arguments go astray. Thomasson (2007) gives independent grounds for thinking that all quantification must at least tacitly presuppose a category or categories of entity over which we are quantifying, and argues that adopting that view provides the uniform basis for dissolving a number of problems supposed to arise with accepting an ontology of ordinary objects.

2.2 The Ryle/Husserl Method of Distinguishing Categories

While those who only make use of the idea of category differences (rather than purporting to offer a category system) have no need to worry about how to provide an exhaustive list of categories, they nonetheless owe an account of the conditions under which we can legitimately claim that two entities, concepts, or terms are of different categories, so that we know when a category mistake is (and is not) being made. Otherwise, they would face the charge of arbitrariness or ad hocery in views about which categories there are or where category differences lie. Yet there is little more agreement about the proper criteria for distinguishing categories than there is about what categories there are.

Ryle famously considered absurdities to be the key to detecting category differences. But although Ryle made the method famous, he apparently derived the idea from Husserl's method of distinguishing categories of meaning (cf. Ryle 1970, 8; Simons 1995, 120; Thomasson 2002, 124–8, and §1.3 above). But while Husserl used syntactic nonsense as a way of detecting differences in categories of meaning (yielding different grammatical categories), Ryle broadened the idea, taking absurdities more widely conceived to be symptoms of differences in logical or conceptual categories (1938/1971, 180). Thus, e.g., the statement “She came home in a flood of tears and a sedan-chair” (Ryle 1949, 22) is perfectly well-formed syntactically, but nonetheless Ryle classifies it as a sentence that is absurd, where the absurdity is a symptom of the fact that the sentence conjoins terms of different categories.

Ryle describes the test for category differences as follows: “Two proposition-factors are of different categories or types, if there are sentence-frames such that when the expressions for those factors are imported as alternative complements to the same gap-signs, the resultant sentences are significant in the one case and absurd in the other” (1938/1971,181)—in other words, two expressions (or rather: what they signify) differ in category if there are contexts in which substituting one expression for the other results in absurdity. This test, of course, provides no way of establishing that two expressions are of the same category (but only that they are not), since there is an infinite number of sentence-frames, and one may always yet be found that does not permit the substitution to be made without absurdity. It also leaves open and merely intuitive the notion of ‘absurdity’ itself; in fact, Ryle concludes his paper “Categories” with the question “But what are the tests of absurdity?” (1938/1971, 184). Ryle's approach was further developed, in a more formal fashion, by Fred Sommers (1959, 1971).

J. J. C. Smart (1953) criticized Ryle’s criterion for drawing category distinctions on grounds that it could apparently be used to establish a category difference between any two expressions whatsoever. “Thus ‘the seat of the—is hard’ works if ‘chair’  or ‘bench’ is put into the blank, but not if ‘table’  or ‘bed’ is. And if furniture words do not form a category, we may well ask what do” (1953, 227). Without a test for absurdity apart from a certain kind of intuitive unacceptability to native speakers, we seem to be left without a means of declaring ‘Saturday is in bed’  to be a category violation but ‘The seat of the bed is hard’  not to be. Bernard Harrison attempts to meet this challenge by distinguishing the sorts of inappropriateness that result from violations of category facts (such as the former) from those that result from mere violations of facts of usage (the latter) (1965, 315–16). The use of the term ‘bed’ could conceivably be extended in ways that would make ‘The seat of the bed is hard’ acceptable (e.g., if beds came to be made with seats), whereas ‘Saturday’ could not conceivably be extended in a way that would make ‘Saturday is in bed’ acceptable—any such attempted ‘extension’ would just involve using ‘Saturday’  homonymously (e.g., as the name for a day of the week and for a person) (1965, 316–18). For further discussion of intersubstitutability approaches to drawing category distinctions, see Westerhoff (2005, 40–59 and 2002, 338–339). Westerhoff (2004) develops a method of distinguishing categories based on substitutability in worldly states of affairs rather than language.

2.3 Fregean Approaches to Distinguishing Categories

Frege treats distinctions in categories as correlates of distinctions in types of linguistic expression. The category of object, for example, is distinguished by reference to the linguistic category of proper name (Dummett 1973/1981, 55–56; cf. Wright 1983, 13 and Hale 1987, 3–4)—i.e., an object just is the correlate of a proper name, where proper names are held to include all singular terms (including singular substantival phrases preceded by the definite article). Broadly Fregean approaches have been more recently developed and defended by Michael Dummett (1973/1981) and Bob Hale (2010).

Hale develops and defends the Fregean idea that “the division of non-linguistic entities into different types or categories [is] dependent upon a prior categorization of the types of expressions by means of which we refer to them” (2010, 403). As he develops the idea, to be an object is “to be the referent of a possible singular term, to be a property is to be the referent of a possible (first-level) predicate, and so on for other cases” (2010, 411). He also argues that this encourages a deflationary approach to existence questions according to which we may argue for the existence of entities of a certain kind by simply arguing “that there are true statements involving expressions of the relevant kind” (2010, 406).

Dummett (1973/1981) also aims to develop and precisify a broadly Fregean approach to category distinctions. Frege leaves the distinction between so-called ‘proper names’ and other parts of speech merely intuitively understood, but Dummett argues that, e.g., one could make a start at criteria for distinguishing proper names by requiring substitutability of terms while preserving the well-formedness of a sentence (which, as we have seen in §1.3, also plays a role in Husserl's distinction of meaning categories), and while preserving the validity of various patterns of inference (where the latter requirement is needed to distinguish proper names from other substantival terms such as ‘someone’ and ‘nobody’) (1973/1981, 58 ff.). (For further refinements of these criteria, see Dummett (1973/1981, 61–73) and Hale (1987, Chapter 2).)

In line with Frege's requirement (1884/1968, §62) that names must be associated with a criterion of identity, Dummett argues that an additional test (beyond these formal tests) is needed to distinguish genuine proper names (to which objects correspond) from other sorts of expression: “Even though an expression passes the more formal tests we devised, it is not to be classified as a proper name, or thought of as standing for an object, unless we can speak of a criterion of identity, determined by the sense of the expression, which applies to the object for which it stands” (1973/1981, 79).

Thus once grammatical categories are distinguished, enabling us to thereby distinguish the logical category object by reference to the linguistic category of proper name, we can go on to draw out category distinctions among objects. To avoid confusion, Dummett calls the first range of distinctions (among logical categories of objects, properties, relations, etc.) distinctions among ‘types’ and the second range of distinctions (within the type object) distinctions among ‘categories’ (1973/1981, 76).

Since, as Dummett argues (in a point further developed in Lowe 1989 and Wiggins 2001), proper names and sortal terms must be associated with a criterion of identity that determines the conditions under which the term may be correctly applied again to one and the same thing (1973/1981, 73–75), we may use the associated criteria of identity in order to distinguish categories of objects referred to. All of those names and general sortal terms (usable in forming complex names) that share a criterion of identity are said to be terms of the same category, even if the criteria of application for the associated sortals vary (1973/1981, 546). Thus, e.g., the sortal terms ‘horse’ and ‘cow’ (similarly, names of horses and cows) are terms of the same category, since they share the identity criteria suitable for animals.

As Lowe (1989, 108–118) notes, this approach to categories blocks certain reductivist moves in metaphysics. For, e.g., if sortal terms such as ‘person’ and ‘organism’ are associated with different identity conditions, then those who seek to reductively identify persons with biological organisms are involved in a category mistake.

The idea that category distinctions among objects may be drawn out in terms of the identity and/or existence conditions associated with terms of each category has recently gained popularity. Though they differ in details, versions of the approach have been utilized not only by Frege, Dummett and Hale but also by Lowe (2006, 6) and Thomasson (2007).

This approach to drawing category distinctions among objects can avoid various potential problems and sources of skepticism. It is not subject to problems like those Smart raised for Ryle’s criterion, for days of the week clearly have different identity conditions than do persons, whereas beds and chairs seem to share identity conditions (those suitable for artifacts). Such a method of drawing out categories also is not subject to the sorts of skepticism raised above for category systems. Here there is no claim to provide an exhaustive list of categories, and for a principled reason: different categories may come into discussion as long as nominative terms or concepts associated with distinct identity conditions may be invented.

Following this method also guarantees that the categories distinguished are mutually exclusive, for it is a corollary of this position that entities may be identified only if they are governed by the same identity conditions (and meet those), so that it is ruled out a priori that one and the same entity could belong to two or more distinct categories, in violation of the mutual exclusivity requirement.

This method of distinguishing categories also provides a principled way of answering some of the central questions for theories of categories, including whether or not there is a single summum genus, and what the relationship is between linguistic/conceptual and ontological categories. Such completely general terms as “thing” “entity” or “object”, on Dummett’s view, are not genuine sortal terms, since they fail to provide any criteria of identity. Thus clearly on this view (as on Aristotle's) there is no summum genus under which categories such as artifact, animal, etc. could be arranged as species, since (lacking criteria of identity) such candidate catch-all terms as ‘object’, ‘being’, ‘entity’ and the like are not even sortal terms and so cannot be categorial terms.

Views that, like the Rylean and Fregean approaches, distinguish categories by way of language, are sometimes criticized as capable only of noting differences in category of certain linguistic expressions. For why, it might be asked, should that have anything to tell us about differences in the categories of real things?

Hale argues that there is no serious alternative to using types of expression that aim at referring to entities of different types if we hope to characterize such basic logical categories (or types) as object and property (2010, 408). For what it is to be an object or property evidently cannot be conveyed merely by ostension, nor by more substantive criteria, without being restrictive in ways the beg the question against various views of what objects or properties there are. Moreover, he argues that we can avoid making our (logical) categories unduly dependent on what language we actually have by treating objects and properties as correlates of possible, not merely actual, expressions of the relevant sorts (2010, 411).

Dummett's way of understanding categories of objects also opens the way for a reply to this objection. For Dummett argues that, without some associated categorial concept, we cannot single out objects (even using names or demonstratives) (1973/1981, 571). Categorial concepts are necessary for us to single out ‘things’ at all, and cannot be derived from considering ‘things’ preidentified without regard to categories. (It would thus follow from this that Johansson’s idea that we could arrive at categories by abstraction from considering individual things would be wrong-headed.) On this view, then, categories not only may but must be distinguished primarily by way of distinguishing the identity conditions criterially associated with the proper use of different sortal terms and names. If we cannot refer to, discover, or single out objects at all except by way of a certain categorial conception (providing application and identity conditions), then the categorial differences in our sortal terms or names (marked by their differences in identity conditions) are ipso facto, and automatically, category differences in the things singled out by these terms—the possibility of a ‘mistake’ here just does not arise, and the connection between the category of an expression used to refer to a given entity and the category of the entity referred to is ensured.