In music, the term period refers to certain types of recurrence in small-scale formal structure. In twentieth-century music scholarship, the term is usually used as defined by the Oxford Companion to Music: "a period consists of two phrases, antecedent and consequent, each of which begins with the same basic motif." Earlier usage varied somewhat, but usually referred to similar notions of symmetry, recurrence, and closure. The concept of a musical period originates in comparisons between music structure and rhetoric at least as early as the 16th century. Western art music In Western art music or Classical music, a period is a group of phrases consisting usually of at least one antecedent phrase and one consequent phrase totaling about 8 bars in length (though this varies depending on meter and tempo). Generally, the antecedent ends in a weaker and the consequent in a stronger cadence; often, the antecedent ends in a half cadence while the consequent ends in an authentic cadence. Frequently, the consequent strongly parallels the antecedent, even sharing most of the material save the final bars. In other cases, the consequent may differ greatly (for example, the period in the beginning of the second movement of the Pathetique Sonata). The 1958 Encyclopédie Fasquelle defines a period as follows: "A complex phrase, in which the various parts are enchained." Another definition is as follows: "In traditional music...a group of bars comprising a natural division of the melody; usually regarded as comprising two or more contrasting or complementary phrases and ending with a cadence." (Harvard Dictionary of Music, 1969) And "A period is a structure of two consecutive phrases, often built of similar or parallel melodic material, in which the first phrase gives the impression of asking a question which is answered by the second phrase." A double period is, "a group of at least four phrases...in which the first two phrases form the antecedent and the third and fourth phrases together form the consequent." When analyzing Classical music, contemporary music theorists usually employ a more specific formal definition, such as the following by William Caplin: "the period is normatively an eight-bar structure divided into two four-bar phrases. [...] the antecedent phrase of a period begins with a two-bar basic idea. [...] bars 3–4 of the antecedent phrase bring a 'contrasting idea' that leads to a weak cadence of some kind. [...] The consequent phrase of the period repeats the antecedent