 In an attempt to reconcile these two strands, one might say that, for Berlin, the values that humans create are rooted in the nature of the beings who pursue them. But this is simply to move the question back a step, for the question then immediately arises: Is this human nature natural and fixed, or created and altered over time through conscious or unconscious human action? Berlin’s answer (see e.g. 1990, 319–23) comes in two parts. He rejects the idea of a fixed, fully specified human nature, regarding natural essences with suspicion. Yet he does believe (however under-theorised, unsystematic and undogmatic this belief may be) in boundaries to, and requirements made by, human nature as we know it. This common human nature may not be fully specifiable in terms of a list of unvarying characteristics; but, while many characteristics may vary from individual to individual or culture to culture, there is a limit on the variation – just as the human face may vary greatly from person to person in many of its properties, while remaining recognisably human, but at the same time it is possible to distinguish between a human and a non-human face, even if the difference between them cannot be reduced to a formula. Indeed, at the core of Berlin’s thought was his insistence on the importance of humanity, or the distinctively human, both as a quasi-Kantian category and as a moral reality, which does not need to be reduced to an unvarying essence in order to have descriptive and normative force.