The word _practice_ refers to a number of different phenomena having this in common, that they occur when the same mental function is frequently repeated, either in immediate succession or with moderately long intermissions. To a large extent practice is identical with the selective and supplementing functions of the mind which are discussed above. But certain effects included in the term _practice_ cannot be understood thus and must be regarded as the signs of a more fundamental law of the mind. Setting aside, however, the distinction between fundamental and secondary regularities of mental function, two facts should be mentioned here. The more frequently the same task is imposed upon our mind, the more perfectly--this is the first fact--is it carried out. But perfection has various aspects. So far as sense perception is concerned, perfection means a lowering of the so-called threshold of perception and of discrimination, especially the latter. Weaker sounds, lights, tastes are perceived; smaller differences of color, tone, weight, movement, size are correctly named. Perfection means also greater quickness of response. The same number of elements is perceived in less time, is memorized or reproduced more quickly. The rapidity of reading, thinking, writing, and other skillful movements is increased. Perfection means, further, an enlargement of the scope of the situation responded to. We are conscious of a greater number of its parts after having perceived a certain thing repeatedly. Of different things a greater number are simultaneously perceived. After repeated performance of a certain act, we take into account a greater number of circumstances and adapt it to them. That a certain activity which has been engaged in repeatedly can be continued longer at one time, may also be mentioned in this connection. So far as definite purposes are concerned, these are accomplished more and more economically and accurately, that is, with less expenditure of energy, with stricter avoidance of unnecessary movements, with a decreasing number of errors.