The passionate intensity of his nature has left its impress on the enunciation of his physical as well as of his moral doctrines. He has a thoroughly logical grasp of his subject as a whole. He shows the capacity of unfolding it and marshalling all his arguments in symmetrical order, and of arranging in due subordination vast masses of details. Vigour in acquiring and tenacity in retaining the knowledge of facts are combined with a high organising faculty. He has also, beyond any other Roman writer, a power of analysing and comprehending abstract ideas, such as that of the infinite, of space and time, of causation and the like, and of keeping the consequences involved in these ideas present to his mind through long-sustained processes of reasoning. He alone among his countrymen possessed, if not the faculty of original speculation, the genuine philosophic impulse, and the powers of mind demanded for abstruse and systematic thinking. This vigour of understanding is displayed in many processes of deductive reasoning, in the power of seizing some general principle underlying diverse phenomena, in the use of analogies by which he illustrates the argument and advances from known to unknown causes and from things within the cognisance of our senses to those beyond their range, and in the clearness and variety of his observation. His system cannot be called either purely inductive or purely deductive, though it is more of the former than of the latter. He argues with great force both from a large and varied mass of facts to general laws and from general principles to facts involved in them. The best examples of his power of following abstract ideas into their consequences may be found in the first two books, where he establishes the existence of vacuum, the infinity of space and of the atoms, the limitations of the form of the atoms and the like. The reasoning at i. 298-328 where the existence of invisible bodies is established affords a good instance of his power of recognising a common principle involved in a great number and variety of phenomena.