What is the eugenic "indication" in Casti Connubii? In Pope Pius XI's encyclical Casti Connubii, we read:

What is asserted in favor of the social and eugenic &quot;indication&quot; may and must be accepted, provided lawful and upright methods are employed within the proper limits

Within the context of paragraph 66, the &quot;indication&quot; (eugenicæ indicationis) is condemned when exploited &quot;for the killing of the innocent&quot;, e.g., abortion (cf. paragraph 63).
But in the larger context,

What is eugenic &quot;indication&quot;? Presumably it is related to &quot;hereditary transmission&quot; of genetic traits (cf. paragraph 68).
What is a lawful employment of this eugenic &quot;indication&quot;?
Arthur Vermeersch, S.J., might have been that encyclical's ghostwriter. He describes the &quot;eugenic indication&quot; in his catechism on that encyclical, What is Marriage? p. 47:


What are some of the opinions that are current on the subject of feticide and abortion?[…] A eugenic reason [or &quot;determining reason&quot; to &quot;allow feticide&quot;] is to prevent the birth of children who would be monstrous or idiotic.


Also, pp. 51-2:


Is eugenic science then to be reprobated?[…] On March 21 of this year (1931) the Holy Office, with the approval of the Holy Father, declared that we must absolutely reject and hold as false and condemned by the Encyclical &quot;Casti Connubii&quot; of December 31, 1930, the so-called &quot;eugenic&quot; doctrine, as well &quot;positive&quot; eugenics as &quot;negative,&quot; together with the means which it indicates for the improvement of the human race, by neglecting the laws of nature, of God, or of the Church, concerning marriage and the rights of individuals. [AAS 32 p. 118]