 That is, in any valid syllogistic inference, the middle term shared by the premises is the warrant for the conclusion. In scientific explanation, however, the middle term must also identify the cause of the fact given in the conclusion—what that term identifies is the causal link between the subject and attribute. To use another of his common examples, if we seek to explain the periodic sound of noise in the clouds, the middle term must identify the cause of the connection between that noise and those clouds. Moreover, on Aristotle’s account of the relationship between causal demonstration and scientific definition, knowing the cause of thunder is at the same time knowing the essence of thunder, what thunder really is.