              Equally central to Aristotle’s thought is his four-causal explanatory scheme. Judged in terms of its influence, this doctrine is surely one of his most significant philosophical contributions. Like other philosophers, Aristotle expects the explanations he seeks in philosophy and science to meet certain criteria of adequacy. Unlike some other philosophers, however, he takes care to state his criteria for adequacy explicitly; then, having done so, he finds frequent fault with his predecessors for failing to meet its terms. He states his scheme in a methodological passage in the second book of his Physics: