Evil would be understood as a par with good. Good is the realization / actualization of a natural end, evil the opposite, that is, the privation of a natural end. Amputation, per se, it's obviously evil since it frustrates the ends of that body part.

Just to confirm, I'm not trolling or anything. This is a real doubt.

Presumably, he means the natural law sense of an immoral and unnatural act, one against the good.

I don't think the OP's question can be answered unless we know the circumstances. Is the amputation because the limb is injured and diseased and may cause death?  

Jeremy Taylor wrote:

Presumably, he means the natural law sense of an immoral and unnatural act, one against the good.

I don't think the OP's question can be answered unless we know the circumstances. Is the amputation because the limb is injured and diseased and may cause death?  

I was thinking more about death (either you amputate it or you die); if anyone wants to talk about an injured limb, I would like to hear about it too.

My understanding is that the natural law tradition sees it as permissible to amputate a limb, or remove an organ, if that is needed to save oné's life, because the ends of the limb are subsumed in the ends of the whole body. But I don't know where the line is drawn about diseased limbs (or organs). I don't think it would be considered permissible if one was someone who had a psychological condition and wished to have the limb amputated for this reason.