 An answer to this ‘disastrous’ history-fed argument was the development of a causal theory of reference, which allows for referential continuity in theory-change. This theory was first suggested by Saul Kripke (1972) as an alternative to the then dominant descriptive theories of reference of proper names and was extended by Putnam (1973, 1975) to cover natural kind terms and theoretical terms. According to the causal theory, the reference of a theoretical term t is fixed during an introducing event in which an entity or a physical magnitude is posited as the cause of various observable phenomena. The term t, then, refers to the posited entity. Though some kind of descriptions of the posited entity will be associated with t, they do not play a role in reference fixing. The referent has been fixed existentially: it is the entity causally responsible for certain effects.