 A second, relatively early, ancestor of contemporary functionalism is Hobbes's (1651) account of reasoning as a kind of computation that proceeds by mechanistic principles comparable to the rules of arithmetic. Reasoning, he argues, is “nothing but reckoning, that is adding and subtracting, of the consequences of general names agreed upon for the marking and signifying of our thoughts.” (Leviathan, Ch. 5) In addition, Hobbes suggests that reasoning — along with imagining, sensing, and deliberating about action, all of which proceed according to mechanistic principles — can be performed by systems of various physical types. As he puts it in his Introduction to Leviathan, where he likens a commonwealth to an individual human, “why may we not say that all automata (engines that move themselves by springs and wheels…) have an artificial life? For what is the heart but a spring; and the nerves but so many strings, and the joints but so many wheels…”. It was not until the middle of the 20th century, however, that it became common to speculate that thinking may be nothing more than rule-governed computation that can be carried out by creatures of various physical types.