Final answer:
Naturalists believe that man is the measure of all things, suggesting that human experiences and perspectives are the basis for defining reality and truth.
Step-by-step explanation:
According to naturalists, man is the measure of all things. This philosophical position emphasizes that human beings are the ultimate source of meaning and value in the universe. By this understanding, it's human experiences, perspectives, and conditions that define reality and truth. The phrase is derived from Protagoras's famous assertion in ancient Greek philosophy.