The Sapir-Whorf hypothesis is a two part hypothesis developed by Edward Sapir and Benjamin Lee Whorf. In its strong form, the hypothesis states that language determines how we think, i.e. if a language does not have a word for a given concept, then speakers of that language will not have access to that concept. In its weaker form, the hypothesis merely argues that if a concept does not have a word in a specific language, the concept will be accessible, but not as easily.

Source:

Hayes, N. (2000) The Foundations of Psychology (3rd edition), (pp.106-108). London: Thomson Learning.