Taking inspiration from a recent posting in the APA style blog, this month's tip addresses when it's appropriate to use the relative pronouns "who" versus "that."
Please consider the following sentence: The researcher that published the article is well-known in the academic community. In this sentence, "that" is used as a relative pronoun to refer to the researcher. However, when referring to people, the appropriate pronoun is "who": The researcher who published the article is well-known in the academic community. Use "that" when referring to animals or inanimate objects; for example, "I am looking for the evidence that will prove my theory", or "the dog that salivated when the researcher rang the bell has been in the study for 5 weeks".