The remainder of the second book is given to the various forms of poetry,--the canzone, the ballata, the sonnet,--and to the rules of versification. The work breaks off unfinished, in the middle of a sentence. There were to have been at least two books more; but, fragment as it is, the treatise is an invaluable document in the illustration of Dante's study of his own art, in its exhibition of his breadth of view, and in its testimony to his own consciousness of his position as the master of his native tongue, and as the poet of righteousness. He failed in his estimate of himself only as it fell short of the truth. He found the common tongue of Italy unformed, unstable, limited in powers of expression. He shaped it not only for his own needs, but for the needs of the Italian race. He developed its latent powers, enlarged its resources, and determined its form. The language as he used it is essentially the language of to-day,--not less so than the language of Shakespeare is the English of our use. In his poetic diction there is little that is not in accord with later usage; and while in prose the language has become more flexible, its constructions more varied and complex, its rhythm more perfected, his prose style at its best still remains unsurpassed in vigor, in directness, and in simplicity. Changeful from generation to generation as language is, and as Dante recognized it to be, it has not so changed in six hundred years that his tongue has become strange. There is no similar example in any other modern literature. The force of his genius, which thus gave to the form of his work a perpetual contemporaneousness, gave it also to the substance; and though the intellectual convictions of men have changed far more than their language, yet Dante's position as the poet of righteousness remains supreme. It is surprising that with such a vast and difficult work as the 'Divine Comedy' engaging him, Dante should have found time and strength during his exile for the writing of treatises in prose so considerable as that on the Common Tongue, and the much longer and more important book which he called 'Il Convivio' or 'Il Convito' (The Banquet). It is apparent from various references in the course of the work that it was at least mainly written between 1307 and 1310. Its design was of large scope. It was to be composed of fifteen parts or treatises; but of these only four were completed, and such is their character both as regards their exhibition of the poet's nature and their exposition of the multifarious topics of philosophy, of science, and of morals treated in them, that the student of Dante and of mediaeval thought cannot but feel a deep regret at the failure of the poet to carry his undertaking to its intended close. But though the work is imperfect as a whole, each of its four parts is complete and practically independent in itself.