In his rhetorical works, Cicero left a legacy of practical instruction to posterity. The treatise "On Invention" is merely interesting as the juvenile production of a future great man. "The Orator," "Brutus, or the illustrious Orators," and "The Orator to Marius Brutus," are the results of his matured experience. They form together one series, in which the principles are laid down, and their development carried out and illustrated; and in the "Orator" he places before the eyes of Brutus the model of ideal perfection. In his treatment of that subject, he shows a mind imbued with the spirit of Plato; he invests it with dramatic interest, and transports the reader into the scene which he so graphically describes.
Roman philosophy was neither the result of original investigation, nor the gradual development of the Greek system. It arose rather from a study of ancient philosophical literature, than from an emanation of philosophical principles. It consisted in a kind of eclecticism with an ethical tendency, bringing together doctrines and opinions scattered over a wide field in reference to the political and social relations of man. Greek philosophy was probably first introduced into Rome 166 B.C. But although the Romans could appreciate the majestic dignity and poetical beauty of the style of Plato, they were not equal to the task of penetrating his hidden meaning; neither did the peripatetic doctrines meet with much favor. The philosophical system which first arrested the attention of the Romans, and gained an influence over their minds, was the Epicurean. That of the Stoics also, the severe principles of which were in harmony with the stern old Roman virtues, had distinguished disciples. The part which Cicero's character qualified him to perform in the philosophical instruction of his countrymen was scarcely that of a guide; he could give them a lively interest in the subject, but he could not mould and form their belief, and train them in the work of original investigation. Not being devoutly attached to any system of philosophical belief, he would be cautious of offending the philosophical prejudices of others. He was essentially an eclectic in accumulating stores of Greek erudition, while his mind had a tendency, in the midst of a variety of inconsistent doctrines, to leave the conclusion undetermined. He brought everything to a practical standard; he admired the exalted purity of stoical morality, but he feared that it was impractical. He believed in the existence of one supreme creator, in his spiritual nature, and the immortality of the soul; but his belief was rather the result of instinctive conviction, than of proof derived from philosophy.