 Specifically, he took a critical look at how the meanings we assign to parts of speech (e.g., verbs naming actions and nouns naming substances) constitute differences in cognition among people.Brown focused on the semantic definition of a noun, which is known as a person, place or thing.The problem that he identified is that there is no definitive meaning of what a thing is, hence, Brown explained that nouns may be the key to understanding how parts of speech affect cognition.