But Onan knew that the offspring would not be his: But is used by Revised Standard Version to contrast what Onan is willing to do with what Judah orders him to do. Onan could not claim as his the children that would be born to him and Tamar. These children would have inheritance rights as the offspring of Er. In some languages this is expressed simply as “Onan knew that the baby would not be his own child.”

So when he went in to his brother’s wife …: when in this context means “whenever,” “each time.” In some languages it may be necessary to say what the Hebrew passes over: “He took [married] the woman, but when….” Brother’s wife may need to be expressed as “dead older brother’s wife.”

He spilled the semen on the ground: spilled translates a verb form meaning to let something go to waste. The action described is of Onan withdrawing his penis before ejaculating his semen, in order to prevent Tamar from becoming pregnant.

Translators must be particularly careful in expressing this act so that it will not cause embarrassment in public reading. If the picture is too graphic, it may be possible to express it more indirectly as in Biblia Dios Habla Hoy: “Therefore, each time he united [sexually] with his brother’s widow, he tried to prevent her from becoming pregnant….” In some languages there are indirect ways of speaking of semen; for example, “he let his strength run out on the ground.” In many languages the term for semen is just omitted in this context, or is indicated by some indefinite word; for example, “he let it fall to the ground.” Another example of a translation that does this also makes clear the action of withdrawal: “he did not spill anything inside that woman … he spilled on the ground.”

Lest he should give offspring to his brother: that is, “in order not to give children to his brother,” “so that his brother would not have children,” or “because he didn’t want the woman to have a baby that would belong to his brother.”

Quoted with permission from Reyburn, William D. and Fry, Euan McG. A Handbook on Genesis. (UBS Helps for Translators). New York: UBS, 1997. For this and other handbooks for translators see here .