Q

Summary

Q. E. D. (clause): an abbreviation of the Latin quod erat demonstrandum “which was to be shown.” Latin quod, like the cognate English what, is from the Indo-European root kwo- that appears in many relative and interrogative pronouns. Latin erat is a past tense of esse “to be”; the underlying Indo-European root es- is also found in native English is. Latin demonstrandum is a type of passive causative that means “to be shown,” from the infinitive demonstrare “to demonstrate, to show.” It is from the Indo-European demonstrative de- plus the root men- “to think.” In order to demonstrate the truth of a proposition you must first think through your argument. In traditional geometry books, after the steps of a proof were listed, the abbreviation Q.E.D. typically appeared at the end in order to indicate that the proposition in question had now been proved. [109, 56, 32, 134, 139]

Q. E. F. (clause): an abbreviation of the Latin clause quod erat faciendum “which was to be done.” Latin quod, like the cognate English what, is from the Indo-European root kwo- that appears in many relative and interrogative pronouns. Latin erat is a past tense of esse “to be”; the underlying Indo-European root es- is also found in native English is. Latin faciendum is a type of passive causative that means “to be done,” from the infinitive facere “to do.” It is from the Indo-European root dhe- “to set.”