 “On God” begins with some deceptively simple definitions of terms that would be familiar to any seventeenth century philosopher. “By substance I understand what is in itself and is conceived through itself”; “By attribute I understand what the intellect perceives of a substance, as constituting its essence”; “By God I understand a being absolutely infinite, i.e., a substance consisting of an infinity of attributes, of which each one expresses an eternal and infinite essence.” The definitions of Part One are, in effect, simply clear concepts that ground the rest of his system. They are followed by a number of axioms that, he assumes, will be regarded as obvious and unproblematic by the philosophically informed (“Whatever is, is either in itself or in another”; “From a given determinate cause the effect follows necessarily”). From these, the first proposition necessarily follows, and every subsequent proposition can be demonstrated using only what precedes it. (References to the Ethics will be by part (I–V), proposition (p), definition (d), scholium (s) and corollary (c).)