I hate to be a bore about this, but it's not a tautology. The "ends justify the means' only if you are a consequentialist, and that's a controversial theory. Anyway, not even then. This is sloppy talk. People should reread the Trotsky-Dewey debate (Their Moral and Ours), in which two parties from different perspectives, both consequentialists who think that what makes an action right is that it promotes the good, agree that good ends do not justify any means whatsoever, and that there are means that undermine any good that might come out of their use. And then there are nonconsequentialists like me who think that in most circumstances there are near-absolute restrictions on means. For example, torture, I believe, is impermissible almost come what may. jks
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I agree that torture is always, under all circumstances, impermissible. I remain a bit sceptical of your route to that conclusion. If you base your argument on the illegitimacy of certain means, in concrete cases agents will find a way to make the immediate situation "different," thus regaining the justification of means through (usually hypothetical) ends. You yourself stick in an "almost" above.
I don't have the philosophical tools to do it with, I think one can dissolve ends/means distinction: That in the case of torture, then, the objection to the torture is that it itself necessarily becomes (part of) the "end." In a regime which by its nature (and not merely aberrantly) is a repressive regime it seems clear to me that the use of torture (as e.g., in the case of what is commonly called merely "police brutality") is an essential part of the regime. And in a regime which is not by its nature repressive, the practice of torture will transform the regime from inside. I see how this can be expressed in terms of ends and means, but I would like to see a better way of expressing it. I think probably that the ends/means category is reductive in some way.
Carrol