The principal metaphysical questions concerning natural kinds are threefold. First, are the kinds that we think of as ’natural’ kinds genuinely natural? Second, do natural kinds have essences? Third, are natural kinds basic ontological entities or are they derived from or reducible to other entities (e.g., universals)? As regards the first question, the general problem is to determine which of the kinds to which science makes appeal, if any, correspond to real natural kinds—those existing in nature, so to speak—and which of these kinds are merely conventional—those whose boundaries are fixed by us rather than nature. As regards the second question, the problem is whether there are properties that might be essential for kind membership. Natural kind essentialists hold that natural kinds have essences (Ellis 2001, 2002, 2005). The essence of a natural kind is a property or set of properties whose possession is a necessary and sufficient condition for a particular's being a member of the kind. That fact is a "so-called" essential fact concerning the kind; it is a fact that, in Fine's terms, stems from the identity or nature of the kind (Fine 1994). Some anti-essentialists argue that there is no non-question begging way of motivating the appeal to essences (Mellor 1977). Mellor argues that the existence of essences in essentialist accounts of natural kinds is simply a gratuitous assumption. (Mellor, 1977: 309). Others use examples from the empirical sciences such as biology to argue that essentialism is too limited to capture the kinds we find in the special sciences (Dupré 1981, 1993) . In particular, essentialist accounts of kinds construe them as immutable or static, whereas examples from the natural sciences delineate mutable and dynamic kinds. Finally, even if we regard natural kinds as genuinely natural and possessing essences, the third question regarding the ontological status of natural kinds remains. One might regard natural kinds as irreducible, basic, sui generis entities (alongside, for example, particulars and universals) (Ellis 2001; Lowe 1998). Alternatively one might adopt some kind of reductionism, e.g., to universals (Armstrong 1978, 1997) or to clusters of properties (Boyd 1991, Millikan 1999).

To understand the problems and project of Aristotle's Metaphysics, it is best to begin with one of his earlier works, the Categories. Although placed by long tradition among his logical works (see the discussion in the entry on Aristotle's logic), due to its analysis of the terms that make up the propositions out of which deductive inferences are constructed, the Categories begins with a strikingly general and exhaustive account of the things there are (ta onta) — beings. According to this account, beings can be divided into ten distinct categories. (Although Aristotle never says so, it is tempting to suppose that these categories are mutually exclusive and jointly exhaustive of the things there are.) They include substance, quality, quantity, and relation, among others. Of these categories of beings, it is the first, substance (ousia), to which Aristotle gives a privileged position.

Wikipedia's category hierarchy forms a graph. It's definitely cyclic (Category:Ethology belongs to Category:Behavior, which in turn belongs to Category:Ethology).

At any rate, did you know that "Chicago Stags coaches" are a subcategory of "Natural sciences"?

A property right (ius in rem, real right) is an abstract legal concept which relates to an object, referred to as “thing” or “res,” or imprecisely, but commonly, “property.” This object of property is a product of legal categorisation; it may be represented by a physical thing or it can be an abstract legal creation itself, as is the case with an intellectual property right. In any event, for the law the “property-object” (whether tangible, intangible or purely intangible) is the product of a legal conceptualisation. The law (private law) creates any res or thing, whether corporeal or not, through the legal concept of real rights. That enables legal recognition of the res in question. The material object (if there is one) only becomes a res in law if real rights are attached to it. Therefore, real rights and res are both “property”, and particularly with (purely intangible) intellectual property, property rights and property objects merge into one. The abstract conceptual res typically has a reifier to make it recognisable in the material world and for the purpose of social interactions. This reifier can be a corporeal object, in which case it is a direct reifier (a table being a direct reifier and incident of a res, chattel), but, for example in case of copyright, a chattel may act not only as direct reifier of the notional personal (moveable) property right (e.g. a canvas of a painting, the score of a symphony, the paper of a manuscript), but also as an indirect reifier of the notional copyright (artistic work, musical work, literary work). The chattel in question represents directly the personal/moveable property (but does not constitute it, because the res remains a legal concept), and, in addition, the chattel represents indirectly the copyright in the work which is expressed and recorded in the chattel in question (a painting, sculpture etc.).

This Article initiates an account of things in the law, including both conceptual things and material things. Human relationships matter to the design of law. Yet things matter too. To an increasing extent, and particularly via the advent of digital technology, those relationships are not only considered ex post by the law but are designed into things, ex ante, by their producers. This development has a number of important dimensions. Some are familiar, such as the reification of conceptual things as material things, so that computer software is treated as a good. Others are new, such as the characterization of material things as conceptual things, so that digital goods become licensable. The regulatory consequences of the thing are increasingly built into the construction of the thing. These developments appear to be poised to envelop things beyond the digital sphere. It may no longer be apt to divide the world cleanly into conceptual and material objects. Things combine features of both. As a result, they can no longer be viewed solely as passive backgrounds against which relation-based legal analysis unfolds. To ensure that society maintains the ability to regulate as broadly as it deems legitimate, law must account for the creation and design of the things that increasingly dominate developments across a variety of legal domains, from intellectual property law to antitrust law to commercial law. The Article describes how things exercise the authority that characterizes classic legal regulation, and it reviews the different mechanisms that legal institutions have used to recognize and differentiate things. Understanding those mechanisms is a step toward appreciating the nature of the regulatory landscape in which both legal institutions and individuals exist.

Proof-of-concept based on vacuuming every Wikipedia article into the Lucene open source search engine to build a text categorisation tool prototype.

The Calais web service allows you to automatically annotate your content with rich semantic metadata, including Entities like People and Companies and Events & Facts like Acquisitions and Management Changes.

Distributed classification systems function at the intersection of individual choices and the shared linguistic/semantic norms of a social group (the folks in folksonomy).

The semantic web has a lot of people working on the technological guts, but very few on the social practices that might make it happen.

I'd say it's a book I'll keep and likely use as a reference but I doubt I'll ever read the whole thing...