Cause and effect

The twenty-third entry is sous-tendre, and an English reader who knows « subtend » has only half of it. Both go back to the Latin subtendere, to stretch beneath, and both began in geometry. A chord sous-tend an arc, the side of a triangle sous-tend the angle facing it, and there the English is exact: a chord « subtends » an arc, and a distant tower subtends a small angle at the eye. Apart from a corner of botany, where a bract subtends a flower, English stopped at that point. French carried the picture out of the textbook. What is stretched underneath holds something up, so sous-tendre became the ordinary learned verb for whatever lies beneath an idea, a policy or a line of reasoning: les hypothèses qui sous-tendent le modèle, la logique qui sous-tend la réforme. The English for that is « underpin », « underlie » or « be the basis of », and never « subtend », which would send a reader off to look for a diagram. The verb conjugates like tendre, so the participle is sous-tendu: un choix sous-tendu par une crainte is a choice driven by a fear nobody has named.