These methods may be grouped into three general classes, as follows: I. METHODS OF CONTINENCE (TOTAL OR TEMPORARY). In the practice of the methods under this class, there is an avoidance of sexual relations between husband and wife, either continuously or for certain periods during which the liability to conception is great. II. METHODS OF SEMI-CONTINENCE. In the practice of the methods under this class, there is a partial manifestation of the sexual relation accompanied by an absence of the manifestation of the procreative functions. III. METHODS OF CONTRACEPTION. In the practice of the methods under this class, the usual manifestations of the sexual relation are observed, accompanied by an avoidance of the union of the male and female elements of reproduction which result in conception. The student of the subject of Birth Control, of course, familiarizes himself or herself with each of the several classes of methods above noted, for the purpose of understanding the characteristic distinctions between them, and the respective advantages and disadvantages of each class. In the following pages each class will be briefly considered, that the student may acquire a general understanding thereof, and may be enabled to reason intelligently concerning them. In this presentation there will be sought a fair statement of each class, without any desire to influence the student for or against either of them. Continence. Continence (which in this special sense means the avoidance of sexual relations between husband and wife), in the strict sense, is based upon the idea that the sexual relation should not be exercised except for the purpose and intent of procreation. In the restricted usage of the term, it refers to the abstinence from sexual intercourse during stated periods in which the liability to conception is greatest.