In the encyclical Casti Connubii, issued on Dec. 31, 1930, Pope pius xi sought to reaffirm the sanctity and dignity of Christian marriage, uphold the integrity of the family and warn against various errors against conjugal union. According to Pius XI, while one may freely choose to marry or not, because marriage is a divine instituted sacrament, the nuptial union is subject to the laws laid down for it by its Divine Author. The right to beget children imposes a corresponding duty to educate them for life here and hereafter, and thus clearly restricts the exercise of this right to the married state, wherein alone this duty can be adequately fulfilled. It is moreover a way of life in which husband and wife sanctify each other through that conjugal fidelity which deserved to be compared to the union between Christ and His Church which He loves "not for the sake of His own advantage, but seeking only the good of His spouse."
Pope Pius XI also warned that the nuptial bond must never be subject to the whims of man or woman to allow them the unbridled liberty of those purely human unions, variously described as "temporary," "experimental," or "companionate." Nor may the obligations arising from the use of the marital right be avoided by the sins of contraception, direct sterilization, and abortion. Without prejudice to the dignity of woman but in support of it, Pius XI condemned the errors of those who profess to free her from what they regard as the burdens of conjugal fidelity, obedience, and love.
Bibliography: pius xi, "Casti connubii" (encyclical, Dec. 31, 1930) Acta Apostolicae Sedis 22 (1930) 539–592, Eng. Catholic Mind 29 (Jan 1931) 21–64. j. l. thomas, The Catholic Viewpoint on Marriage and the Family (Garden City, N.Y. 1958). e. w. o'rourke, Marriage and Family Life (Champaign, Ill. 1956). j. e. kerns, The Theology of Marriage (New York 1964).
"Casti Connubii." New Catholic Encyclopedia. . Encyclopedia.com. (September 22, 2018). http://www.encyclopedia.com/religion/encyclopedias-almanacs-transcripts-and-maps/casti-connubii
"Casti Connubii." New Catholic Encyclopedia. . Retrieved September 22, 2018 from Encyclopedia.com: http://www.encyclopedia.com/religion/encyclopedias-almanacs-transcripts-and-maps/casti-connubii