 Psycho-functionalism, therefore, can be seen as straightforwardly adopting the methodology of cognitive psychology in its characterization of mental states and processes as entities defined by their role in a cognitive psychological theory. All versions of functionalism, however, can be regarded as characterizing mental states in terms of their roles in some psychological theory or other. (A more formal account of this will be given in Section 4.1 below.) What is distinctive about psycho-functionalism is its claim that mental states and processes are just those entities, with just those properties, postulated by the best scientific explanation of human behavior. This means, first, that the form of the theory can diverge from the “machine table” specifications of machine state functionalism. It also means that the information used in the functional characterization of mental states and processes needn't be restricted to what is considered common knowledge or common sense, but can include information available only by careful laboratory observation and experimentation. For example, a psychofunctional theory might be able to distinguish phenomena such as depression from sadness or listlessness even though the distinctive causes and effects of these syndromes are difficult to untangle solely by consulting intuitions or appealing to common sense. And psychofunctional theories will not include characterizations of mental states for which there is no scientific evidence, such as buyer's regret or hysteria, even if the existence and efficacy of such states is something that common sense affirms.