One other technical peculiarity of the music of the polyphonic period deserves notice here, as it involved a principle destined to assume great importance in later stages of art. The polyphonic writers often introduced successive voices with an identical formula of notes, which by repetition came to have somewhat the virtue of a motif or subject in giving to the music rationality and sequence. They had not as yet, to be sure, enough experience in composing definite themes strictly measured in time to make these embryonic motifs either very long or very distinct, but they did make and utilize subjects striking enough to be remembered and recognized. In this way they introduced the important device of “Imitation.” This imitating of one part by another, even when crudely carried out, gave a certain air of intention and fore-thought to what without it would have been a haphazard utterance of tones, and in later times, when developed to a high pitch of perfection in the fugue and allied forms, became a powerful agent for securing intelligibility. Meanwhile, as we have seen, the intelligibility of the sixteenth-century music depended chiefly on the fine melodic cogency and expressiveness of its individual voice parts. Although time-measurement was well understood, melody was without metrical structure and rhythmic organization. Harmony was the art of making pleasant sounds by bringing the voices together, at prominent moments, on consonant chords; it took no heed of chord relation, of tonality, or of orderly modulation; and it used dissonance with extreme conservatism. Such, in sum, were the most notable technical peculiarities of that polyphonic period which Palestrina brought to its culmination.