  A science is defined by the genus or kind it studies and by a group of specifiable properties which belong to that kind. Secondly, the properties studied within a science are defined in terms of the genus of the science (per se2). Hence, it follows that it will commonly be impossible to prove one thing using a different science. For one would have to prove that a property within one genus applies to a completely different genus. Hence, every science is autonomous. Aristotle makes this claim, however, in the context of his rejection of Plato's view that sciences are subordinate to knowledge of the Good. What he actually claims is much more modest. If one genus comes under another genus, it will be possible, in some cases incumbent, to prove that a property belongs to a genus by using a theorem from another science. In such a case the one science is said to be under (subalternate with) the other science. 