 Fascinating as these questions are in their own right, Epicurus himself does not proceed by creating an abstract model, exploring its internal coherence, and determining its applicability to phenomena, in the ideal manner of modern science. Rather, he begins with the testimony of the senses, which he thinks are always reliable. These provide a basis on which to draw conclusions either with respect to things that still await confirmation or those that are by nature imperceptible (Letter to Herodotus = LH 38). Thus, in beginning his account of the physical world in this Letter, he argues that things cannot arise out of nothing, since otherwise there would be no need of specific seeds for specific plants and animals, and anything whatsoever could be generated out of just any types of material elements. Since this is not seen to happen, but reproduction in things we can observe with our senses is in fact orderly and determinate, spontaneous generation at any level is ruled out. The logic is what Epicurus calls counterwitnessing: a hypothetical premise (here, that things sometimes arise out of nothing) is eliminated because experience tells against its conclusion (here, that the coming into being of visible objects does not require determinate seeds or materials). More simply, if A then B; but not B, hence not A. One might, of course, challenge the implication: something might arise from nothing, even if there are no cases of chickens giving birth to horses. The important point, however, is that Epicurus invokes the data of perception to testify for or against the nature of elementary phenomena; he assumes a certain uniformity of nature at all levels. So too with his next postulate: things are not destroyed into what is not, since in that case everything would cease to exist (and would have ceased to exist before now, given infinite past time — recall that nothing is created out of nothing); but things do exist, hence the premise is false.