A convention is a principle or proposal which is adopted by a group of people, either by explicit choice, as in Sweden's decision to drive on the right-hand side of the road, or as a matter of custom, whose origins are unknown and unplanned, as in the convention of placing forks on the left and knives on the right. The crucial point, though, is that conventions are not forced on us by nature and could, if we collectively wished, be changed. In a certain sense, then, conventions are manifestations of human freedom.
Conventionalism is a view about the status of theories in science.
Linked to instrumentalism and positivism , it urges us to regard deep-level theories about the nature of the world as chosen by us from among many possible alternative ways of explaining the observable phenomena. Theories such as Newton's laws or quantum theory which purport to reveal the underlying structure of the world are not directly provable or disprovable by observation or experiment. They are freely chosen conventions, which may be maintained in the face of apparent counter-evidence. He thought that such deep-lying principles in science are similar to particular sets of geometrical axioms, in that they are chosen to fit a particular range of phenomena. Where conventionalists differ from their opponents is not so much on the element of choice in scientific theorizing, or, if it is, it turns out to be only a matter of degree.