A reductionist holds that the facts or entities apparently needed to make true the statements of some area of discourse are dispensable in favour of some other facts or entities. Reductionism is one solution to the problem of the relationship between different sciences. Thus one might advocate reducing biology to chemistry, supposing that no distinctive biological facts exist, or chemistry to physics, supposing that no distinctive chemical facts exist (see also unity of science). Reductionist positions in philosophy include the belief that mental descriptions are made true purely by facts about behaviour (behaviourism), that statements about the external world are made true by facts about the structure of experience (phenomenalism), that statements about moral issues are really statements about natural facts (naturalism), and many others. Reductionism is properly speaking not a form of scepticism (for the claims in the reduced area may be true and known to be true: indeed, one purpose of the reduction will typically be to show how this is so). Nor is it necessarily a form of anti-realism (see realism/anti-realism), although it is often classified that way. Reductionist claims were popular in the earlier years of analytic philosophy, and were pursued by such writers as Russell and Carnap in the form of programmes of translating the theses from the target science or discourse into theses from the domain to which it was to be reduced. Subsequent recognition of the holism of meaning, and the apparent failure of these reductionist programmes, switched attention to other ways of obtaining the benefits of reduction without incurring the costs of providing the promised translations. See supervenience.