Actually I’m going to save you the effort and provide the cite myself:
… if we were to be at all times punctiliously truthful we might often become victims of the wickedness of others who were ready to abuse our truthfulness. If all men were well-intentioned it would not only be a duty not to lie, but no one would do so because there would be no point in it. But as men are malicious, it cannot be denied that to be punctiliously truthful is often dangerous… if I cannot save myself by maintaining silence, then my lie is a weapon of defense.
(Lectures on Ethics)
Specifically, in the Metaphysics of Morals, Kant states that “not suffer[ing our] rights to be trampled underfoot by others with impunity” is a perfect duty of virtue.
I don’t see how lying to the murderer fails the test you quote, yet Kant does forbid it elsewhere
Truthfulness in statements that cannot be avoided is the formal duty of man to everyone, however great the disadvantage that may arise therefrom for him or for any other.
ETA: perhaps it’s OK to lie out of love of money, but not out of love of man?
Added, years later: by “love of money,” I mean that Kant says that it is OK to lie to the thief, but not to the murderer.
We’re allowed self-defense and punishment, according to Kant (indeed, it is required). It may, for example, be acceptable to lie to a murderer if he lies to you, since we are obligated to punish those who violate the CI. (EDIT: It could also mean that we don’t have to say anything to murderers, we aren’t obligated to tell the truth in every situation, but we are obligated to tell the truth in every case where we tell something. )
That said, I’m not not sure exactly what you mean by the original line “Kant only defended the duty not to lie out of philanthropic concerns”. It could mean, “Kant defended the duty not to lie, but his reasons for this duty were mere philanthropic ones.” It could also mean “With respect to truth-telling, Kant only says we have a duty when we might prefer to lie for philanthropic reasons.” Both interpretations are wrong. Here is a quote from Kant’s explicit tackling of the issue in the appropriately titled “On a supposed right to lie from philanthropy.” Apologies for the long quote but I don’t want to have to debate context.
Truthfulness in statements that one cannot avoid is a human being’s duty to everyone, however great the disadvantage to him or to another that may result from it… If I falsify… I… do wrong in the most essential part of duty in general by such falsification… that is, I bring it about, as far as I can, that statements (declarations) in general are not believed, and so too that all rights which are based on contracts come to nothing and lose their force; and this is a wrong inflicted upon humanity generally… For a lie always harms another, even if not another individual, nevertheless humanity generally, inasmuch as it makes the source of right unusable. ---- “On a supposed right to lie from philanthropy”, Berliner Blätter, September 1797
Actually I’m going to save you the effort and provide the cite myself:
Specifically, in the Metaphysics of Morals, Kant states that “not suffer[ing our] rights to be trampled underfoot by others with impunity” is a perfect duty of virtue.
I don’t see how lying to the murderer fails the test you quote, yet Kant does forbid it elsewhere
ETA: perhaps it’s OK to lie out of love of money, but not out of love of man?
Added, years later: by “love of money,” I mean that Kant says that it is OK to lie to the thief, but not to the murderer.
We’re allowed self-defense and punishment, according to Kant (indeed, it is required). It may, for example, be acceptable to lie to a murderer if he lies to you, since we are obligated to punish those who violate the CI. (EDIT: It could also mean that we don’t have to say anything to murderers, we aren’t obligated to tell the truth in every situation, but we are obligated to tell the truth in every case where we tell something. )
That said, I’m not not sure exactly what you mean by the original line “Kant only defended the duty not to lie out of philanthropic concerns”. It could mean, “Kant defended the duty not to lie, but his reasons for this duty were mere philanthropic ones.” It could also mean “With respect to truth-telling, Kant only says we have a duty when we might prefer to lie for philanthropic reasons.” Both interpretations are wrong. Here is a quote from Kant’s explicit tackling of the issue in the appropriately titled “On a supposed right to lie from philanthropy.” Apologies for the long quote but I don’t want to have to debate context.