Sentence:  Pope Pius 12 , declared in 1951 that it is possible to be exempt from the normal obligation of parenthood for a long time and even for the whole duration of married life , if there are serious <WSD>reasons</WSD> , such as those often mentioned in the so-called medical , eugenic , economic and social `` indications '' . 
Meaning of the word marked with <WSD> tags:  a rational motive for a belief or action