 The chief claim made by all varieties of conventionalism is that facts about the structure of the world are in some sense dependent on human beings, their concepts and their activities in society. The denial of this view, which we will examine in Section 1.2, is the claim that facts about the world are independent of human beings, their concepts and their activities, that is, that there are real independent natural kinds in the world. The claim that scientific facts about the world are dependent on human activity has been analysed in different ways by constructivists. Kukla (2000, Ch. 3) distinguishes (i) material, (ii) causal, and (iii) constitutive dependence. The first, and weakest, claim is material dependence, namely that scientific entities are constructed by the activities of scientists in the laboratory. Chemical reactions are brought about by scientists in the laboratory using purified chemicals in a controlled environment (Knorr-Cetina et al. 1983). The resultant kinds are merely the constructs of this highly artificial environment, along with the pragmatic interests of the scientists (i.e., what they are testing for and the methodology they choose to use). However, it is clear that scientists still abstract from a complex reality and in some circumstances the materials used are purifications of some naturally occurring materials. Indeed, material dependence is a rather weak kind of conventionalism and could even be made compatible with some versions of naturalism/realism (cf. Hacking 1983). Therefore, no general conclusion may be drawn about the natural world and its kinds, from the fact that scientists study scientific kinds in a highly idealized and controlled setting. The second element in Kukla’s three-fold distinction is causal dependence, which occurs when the relevant facts are caused to be true by the fact that they are believed to be true (e.g. belief that there will be a run on the bank can cause a run on the bank, Merton 1948). Hacking’s (1995) human, interactive kinds, such as person with multiple-personality disorder, may be regarded as instances, where the kind and its members are brought into existence by the belief that there are such kinds and people do belong to them. Lastly, the constitutive dependence thesis claims that convention is constitutive of the physical facts. Plausibly, conventions exist in virtue of people holding that they do. Woolgar’s constructivism is of the type that treats all scientific facts like conventions in this respect.