Full Idea
A duty is that on the part of one being which corresponds to the rights of another. Where there are no rights there are no duties. To tell the truth is therefore a duty, but only to the one who has the right to the truth.
Gist of Idea
There are only duties if there are rights, so truth is only for those with a right to it
Source
Benjamin Constant (On Political Reactions [1797], p.123), quoted by Immanuel Kant - On a supposed right to lie p.28
Book Reference
'Deontology', ed/tr. Darwall,Stephen [Blackwell 2003], p.28
A Reaction
We can't claim a right to have all questions answered truthfully (because there is a right to privacy), but we might claim a right not to be lied to (as long as we accept a refusal to answer). Kant rejected this idea.