This paper attempts to specify the ways in which bilingualism might affect cognitive functioning. Two general ways, the "linguistic" and the "non-linguistic," are distinguished. Linguistic explanations explain the effects of bilingualism on cognition as a direct result of the fact that the bilingual has access to two verbal codes. Non-linguistic explanations account for these effects by reference to factors which are extrinsic to, or by-products of, the fact that the bilingual has access to two verbal codes. For example, the greater amount of social interaction which is presumably involved in learning two languages at an early age has been invoked to explain the bilingual's higher level of concept formation. The validity of Macnamara's (1970) theoretical analysis of bilingualism and thought is considered in the light of this distinction. (Author)