matter of a definition actually exists.254 Definition and evidence, consequently presuppose one another. One immediate question springs forth: How is it possible to combine the cause and the caused in a single definition? Through induction? No, for induction only tells us of that which exists. But, it is moreover, impossible to create a definition by classification.255 Aristotle thus concludes that the definition is determined by the combination of the particular among the common in order to establish the universal, which in turn is subdivided into species until one arrives at the individual concepts of which one will provide the definition.256 In order to determine the validity of the definition it becomes necessary to investigate the causes behind the definition. Those causes, according to Aristotle, are the following: 1) “Väsensbegreppet”; 2) “den logiska grunden”; 3) “den verkande orsaken”; and 4) “ändamålet”.257 Of these causes 1) and 2) coincide, and make up one cause.And since the definition (and the knowledge of the causes) refers to an inductive material Hägerström is thus compelled to ask how the definition can indicate the formal cause, the efficient cause as well as the teleological cause, irrespective of the fact that the definition itself has its basis in induction and experience, which only indicates a thing’s existence, but not its essence.258 Aristotle tries to avoid and circumvent this problem by introducing a philosophical distinction between species and genus, of which the latter is more real (in the Aristotelian sense) than the former, since on the one hand, the species constitutes the material of the genus, and on the other, the genus constitutes the form of the species.259 The idea that there exists different degrees of rea ca l l f o r s c i e n t i f i c p u r i t y 117 254 Ibid., pp. 62-63. 255 Ibid., p. 63. 256 Ibid., pp. 63-64. 257 Ibid., p. 64. “Väsensbegreppet” = the material cause, “den logiska grunden” = the formal cause,“den verkande orsaken” = the efficient cause, and finally “ändamålet” = the teleological cause. 258 Ibid., p. 65. 259 Ibid.