In the process of evolution towards a stable form of movement, Dr. Petzoldt recognizes briefly two factors, "Tendency and Competition."[102] Tendency is defined, in general, as the direction, actual or potential, of material parts or of mental or physical function; competition, as the conflict of tendencies, from which a tendency of a higher order results. "The concept of Competition is, like that of Tendency, to be taken in a general significance. A number of forces which act upon a single point compete. Different mental images, observations, concepts, laws, come into competition, from which result concepts and laws of lower and higher orders. The struggle for existence is only a special case of competition. Though this often ends with the immediate or gradual destruction of systems entering upon it, nevertheless only a middle worth between all the competing tendencies can be ascribed to the resultant. Even the conqueror is, after the struggle, other than what he was before it; a part of the tendency destroyed by him lives on in him, has combined with his original tendency to a resultant. Tendencies can as little disappear without compensation as can forces, whether the compensation consists in a strengthening or in a weakening of others, and the _conservation of competing tendencies_ might be regarded as a further qualitative addition to the law of the conservation of force. Hence, in the examination of the effects of the struggle for existence, the like claim of all tendencies taking part in it is not to be left out of consideration. Each makes its full force felt. But not all attain to competition; of the numerous tendencies bound up in one organism, only a few unite, in the single case, to a resultant, which has a direction towards a definite issue." The less the opposition of competing tendencies of concepts or laws, the less the deviation of the resultant from its components, and the less the change these have to undergo. The higher concepts and laws are, the less are the number of distinguishing marks which they take from all single conceptions; for they are the resultants of very strongly opposed components.[103]