Now the fundamental principle of division in philosophical opinion lies in the place assigned to reason in human nature.[12] According to one theory, man is essentially a sensitive subject, though able to reason about his sensations--that is, to associate, compound, and compare them. He is supposed to be built up of sense-presentations associated with feelings of pleasure and pain. Recipient of external impressions which persist in idea and are accompanied by pleasure or pain on his part, and thus followed by other ideas and impressions, man's mental constitution is explained without attributing to reason any spontaneous or productive function.[13] The other view differs from this in attributing spontaneity to reason--making it, in one way or another, the source of forms of thought, principles, or ideas. The former may be called the Naturalistic, the latter the Rationalistic view of man: from that follows a Naturalistic or Natural ethics, from this a Rationalistic or Rational ethics. Into both these theories, in a theoretical as well as in an ethical aspect, the historical turn of thought which has characterised recent inquiry has introduced a profound modification. On the basis of Naturalism, we may either look upon man as an individual distinct from other individuals, as was done by Epicurus and Hobbes and the materialists of the eighteenth century, or we may consider the race as itself an organism, apart from which the individual is unintelligible, and look upon human nature as having become what it now is through a long process of interaction between organism and environment, in which social as well as psychical and physical facts have influenced the result. This is the view to the elaboration of which Comte and Darwin and Spencer have in different ways contributed.[14] What makes the historical method of importance philosophically, is not the mere fact that it traces a sequence of events in time, but the fact that, by doing so, it is able to look upon each link in the chain of events as necessarily connected with every other, and thus to regard as a system--or, rather, as an organism--what previous empirical theories had left without any principle of unity. [Sidenote: Rationalism either individualistic] [Sidenote: or universalistic.]