Ethics and morals

The fortieth entry is a reciprocidade, and the Latin word behind it describes a movement rather than a virtue. Reciprocus was built out of the two smallest directional pieces the language had, re-, backwards, and pro-, forwards, and it was used of whatever runs one way and then comes back again. Nothing in it says anything about kindness, or about a debt owed. That is worth holding on to, because English has quietly kept the mechanical half of the word in one place and the moral half in another. A « reciprocal » in arithmetic is what you get by turning a fraction over; a « reciprocating » engine is one whose piston travels up and then down again; a trade agreement is « reciprocal » when each side gives and each side receives. Portuguese runs both lives through recíproco and a reciprocidade without ever splitting them, and it keeps a plain verb for the returning half, retribuir. So the sentence of this list, A reciprocidade mantém o grupo unido, is closer to the piston than it looks: what holds the group together is not goodwill but the fact that something goes out and something comes back.