=155.= The list of ‘common notions’ is doubtless not limited to the high philosophical principles which we have mentioned; for instance it must include such mathematical principles as ‘two and two make four,’ ‘a straight line is the shortest distance between two points,’ ‘a three-sided figure has three angles,’ and so forth. With these however we have little direct concern. Of more interest to us is another kind of perception[69] recognised by the Stoics as well as by other schools of philosophy, that called the ‘inward touch’ (ἐντὸς ἁφή)[70]. By this the soul becomes aware of its own workings, most obviously of its pleasure and pain. The doctrine of the ‘inward touch’ is of great philosophical importance, for it breaks down the dualism of subject and object, the barrier between the knowing and the known. Since these are the same in the specific cases named, the door is open to the conclusion that everywhere there is a kinship between the two, and that without this knowledge would be without firm foundation. By this kinship we may also explain the fact that direct communications are made by the deity to man, as by dreams, oracles and augury[71]. [Sidenote: Knowledge; the parts and the whole.] =156.= Thus it appears that the elements of knowledge, according to the Stoics, are sensations, perceptions, conceptions or notions, and general or inborn notions. As in the other parts of the Stoic philosophy, we shall regard this fourfold division as indicating generally the ground covered, and not as setting up definite lines of demarcation. The same material may be analyzed from other points of view, as for instance in the study of words, in which we shall find a division into objects, statements, conditional statements, and syllogisms. The elements may also be combined in various ways. A combination or ‘system’ (σύστημα) which is directed towards a useful or pleasurable object, such as music or grammar, is called an ‘art’ (τέχνη, _ars_)[72]; and arts are attainable by ordinary men. The wise man, on the other hand, is not necessarily acquainted with the several arts; his practice is to ‘keep quiet’ when matters are discussed which require such special knowledge. The combination of all knowledge in one all-embracing system is ‘science’ (ἐπιστήμη, _scientia_); the only science in the full sense is philosophy[73]; and in this system no part can be at variance with any other part[74]. The elements of knowledge also acquire the character of science, when they are found to be parts of this compacted system, and therefore incapable of coming into conflict with any other part[75]; and in particular we find the term ‘science’ predicated of comprehensions which are firmly established and cannot be refuted by any argument[76]. In the language of Zeno’s simile, over the closed fist that grasps the object is placed the other hand, keeping it with firmness and assurance in its place[77]; or, to use a comparison first suggested in ridicule of