The sugya is Kiddushin 49b–50a. Devarim she-be-lev eynam devarim literally translated is: ‘words in the heart (= the mind) are not words’. As a technical, legal term the meaning is: if, in any contractual arrangement, there are mental reservations contrary to its verbal or practical implications, these reservations are disregarded.

The sugya is appended to a Mishnah which reads: ‘If a man betroths a woman, stating as a condition “that I am a priest” [i.e. he assures her that she is being betrothed by a member of a priestly family, the aristocracy] and he is found to be [only] a Levite [belonging to a lower social class] or [he states that] he is a Levite and he is found to be a priest [she may not wish to marry into the higher social class]; a Nathin [a Gibeonite, a bastard according to Rabbinic law] and he is found to be a mamzer [a bastard according to Biblical law] or a mamzer and he is found to be [only] a Nathin; a resident in a small town and he is found to be a resident of a large town or a large town and he is found to be of a small town; “on the condition that my house is near to the bath-house” and it is found to be distant, or distant and it is found to be near [and she may not want to live too near to the bath-house]; on the condition that he has a daughter or an adult slave-girl and he has none, or that he has none and is found to have; on the condition that he has no children and he has; or on the condition that he has children and he has none; in all these cases the betrothal is invalid even if she [subsequently] stated: “It was my intention [lit. ‘in my heart’] to be betrothed unto him” [regardless of his status or condition].