Philip Sidney. It is the chief merit of Fracastoro's dialogue, that even while emphasizing this Platonic element, he clearly distinguishes and defines the ideal element in aesthetic imitation. About the same time, in the public lectures of Varchi (1553), there was an attempt to formulate a more explicit definition of poetry on the basis of Aristotle's definition[48] of tragedy. Poetry, according to Varchi, is an imitation of certain actions, passions, habits of mind, with song, diction, and harmony, together or separately, for the purpose of removing the vices of men and inciting them to virtue, in order that they may attain their true happiness and beatitude.[49] In the first place, poetry is an imitation. Every poet imitates, and any one who does not imitate cannot be called a poet. Accordingly, Varchi follows Maggi in distinguishing three classes of poets,--the poets _par excellence_, who imitate in verse; the poets who imitate without using verse, such as Lucian, Boccaccio in the _Decameron_, and Sannazaro in the _Arcadia_; and the poets, commonly but less properly so called, who use verse, but who do not imitate. Verse, while not an essential attribute of poetry, is generally required; for men's innate love of harmony, according to Aristotle, was one of the causes that gave rise to poetic composition. Certain forms of poetry however, such as tragedy, cannot be written without verse; for "embellished language," that is, verse, is included in the very definition of tragedy as given by Aristotle.