Dictionary of Theories, Laws, and Concepts in Psychology

PANDEMONIUM MODEL/THEORY. See PATTERN/OBJECT RECOGNITION THEORY.

PANUM PHENOMENON. See PERCEPTION (I. GENERAL), THEORIES OF.

PAPEZ-MacLEAN THEORIES. See EMOTIONS, THEORIES/LAWS OF.

PARALLELISM/PSYCHOPHYSICAL, THEORY/DOCTRINE OF. See MIND–BODY THEORIES.

PARALLEL LAW. See FECHNER’S LAW.

PARSIMONY, LAW/PRINCIPLE OF. = Lloyd Morgan’s/Morgan’s canon = Occam’s razor = economy, principle of. The law of parsimony states that if two scientific propositions or two theories are equally tenable, the simpler one is to be preferred. Another name for this law is called Lloyd Morgan’s canon in honor of the English zoologist/physiologist Conway Lloyd Morgan (1852–1936). Morgan articulated the principle in 1894 and cautioned against the explanatory excesses of the emerging field of comparative psychology by stating that in interpreting an animal’s behavior, it is always preferable to adopt the psychologically simplest interpretation. Thus, Morgan’s canon refers to the use of a lower, more ‘‘primitive’’ explanation of phenomena than to assume the activity of a higher, more ‘‘mentalistic’’ functioning (cf: Romanes’, 1884, tendency to anthropomorphize animals’ behavior). The canon was very influential in the development of the early behaviorists’ programs and doctrines such as those proposed by Watson (1919) and Thorndike (1898). During Morgan’s time, when the proof of Darwin’s evolutionary theory was uppermost in the minds of

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