Spiro argues that Freud was correct in relation to the different functions he attributed to the primary and secondary processes. However, he asserts that Freud's delineation of formal differences between these two types of mental functioning is critically flawed. Some of the important things that characterize the representation of unconscious thought characterize the representation of conscious thought as well. The author's argument distinguishes between various kinds of representation— indices, icons, and symbols. When cultural symbols represent figurative meanings, they are called tropes, and he distinguishes between cultural tropes and private tropes. He argues that when the term displacement (sign substitution) is used to represent conscious thoughts, it should be called a trope. If it is used to represent unconscious thoughts, it should be designated as defense.