Ramsey, Frank Plumpton (1903–30)

Before Ramsey died at the age of 26 he did an extraordinary amount of pioneering work, in economics and mathematics as well as in logic and philosophy. His major contributions to the latter are as follows. (1) He produced the definitive version of Bertrand Russell’s attempted reduction of mathematics to logic. (2) He produced the first quantitative theory of how we make decisions, for example about going to the station to catch a train. His theory shows how such decisions depend on the strengths of our beliefs (that the train will run) and desires (to catch it), and uses this dependence to define general measures of belief and desire. This theory also underpins his claim that what makes induction reasonable is its being a reliable way of forming true beliefs, and it underpins his equation of knowledge generally with reliably formed true beliefs. (3) He used the equivalence between believing a proposition and believing that it is true to define truth in terms of beliefs. These in turn he proposed to define by how they affect our actions and whether those actions fulfil our desires. (4) He produced two theories of laws of nature. On the first of these, laws are the generalizations that would be axioms and theorems in the simplest true theory of everything. On the second, they are generalizations that lack exceptions and would if known be used to support predictions (‘I’ll starve if I don’t eat’) and hence decisions (‘I’ll eat’). (5) He showed how established, for example optical, phenomena can be explained by theories using previously unknown terms, like ‘photon’, which they introduce. (6) He showed why no grammatical distinction between subjects like ‘Socrates’ and predicates like ‘is wise’ entails any intrinsic difference between particulars and universals.