A final intellectual source in the 1950s and early 1960s was the field then called mechanical indexing, now known as information retrieval. In what became known mechanical indexing as the vector space model for information retrieval (Salton 1971 , Sparck Jones 1986 , researchers demonstrated new ways to define the meaning of words in terms of vectors (Switzer, 1965) , and refined methods for word similarity based on measures of statistical association between words like mutual information (Giuliano, 1965) and idf (Sparck Jones, 1972) , and showed that the meaning of documents could be represented in the same vector spaces used for words. Some of the philosophical underpinning of the distributional way of thinking came from the late writings of the philosopher Wittgenstein, who was skeptical of the possibility of building a completely formal theory of meaning definitions for each word, suggesting instead that "the meaning of a word is its use in the language" (Wittgenstein, 1953, PI 43) . That is, instead of using some logical language to define each word, or drawing on denotations or truth values, Wittgenstein's idea is that we should define a word by how it is used by people in speaking and understanding in their day-to-day interactions, thus prefiguring the movement toward embodied and experiential models in linguistics and NLP (Glenberg and Robertson 2000, Lake and Murphy 2021, Bisk et al. 2020, Bender and Koller 2020).