The hypothesis of linguistic relativity, also known as the Sapir–Whorf hypothesis , the Whorf hypothesis, or Whorfianism, is a principle suggesting that the structure of a language influences its speakers' worldview or cognition, and thus people's perceptions are relative to their spoken language. Research has produced positive empirical evidence supporting linguistic relativity, and this hypothesis is provisionally accepted by many modern linguists.

Many different, often contradictory variations of the hypothesis have existed throughout its history. The strong hypothesis of linguistic relativity, now referred to as linguistic determinism, says that language determines thought and that linguistic categories limit and determine cognitive categories. This hypothesis was held by some of the early linguists before World War II. This version is generally agreed to be false by modern linguists.

Although common, the term "Sapir–Whorf hypothesis" is considered a misnomer by linguists for several reasons: Edward Sapir and Benjamin Lee Whorf never co-authored any works, and never stated their ideas in terms of a hypothesis. The distinction between a weak and a strong version of this hypothesis is also a later development; Sapir and Whorf never set up such a dichotomy, although often their writings and their views of this relativity principle are phrased in stronger or weaker terms.

The principle of linguistic relativity and the relationship between language and thought has also received attention in varying academic fields from philosophy to psychology and anthropology, and it has also inspired and colored works of fiction and the invention of constructed languages.