Early explanations of sound change were often sought in extralinguistic factors such as climate or the speakers' physiology. More recently, scholars have been reluctant to explain changes this way, but the most widely accepted extralinguistic explanation is the substratum theory. Other linguists, notably the Prague group, looked to the linguistic system itself for causes of sound change. Skepticism at ever finding explanations was expressed by generative grammarians. A landmark in this discussion came when R. Lass (1980) suggested that to explain change was to predict it, which is impossible. Subsequently, an approach that looks at both internal and external factors has gained favor. Four uses of the term "explanation" exist: a general historical one; an approach suggesting the universal nature of sound change; explanation having predictive power; and, most commonly, explanation of specific changes. The fact that language is subject to variation does not explain sound change, but does point to its possible origin. Variants may be idiosyncratic and not spread, or may find their way into the linguistic system. Language-specific explanations entail other issues. Explanations of sound change can be given as long as it is realized that they merely connect phenomena to their effects. Contains 57 references. (MSE)