Recently I was trying to talk someone out of suicidal thought and he replied along the lines of "no one asked for my permission when they brought me to this world so it's my right to leave without their permission". Thank god he didn't actually do it but does that argument carry any weight? Would a philosopher be persuaded? If so surely anyone could freely commit suicide?

There's a fine book by Jennifer Hecht called "Stay," that outlines the many different positions philosophers have taken on the topic. It's a fascinating read. For myself, I don't wholly agree with your friend's claim. I do partially agree in that I think individual autonomy, including autonomy in the decision to end one's own life, should be valued a great deal and overridden only for very good reasons. There are, however, some very good reasons to override the choice of suicide in many circumstances (not all). Here are two I find compelling: (1) obligations to our future selves and (2) the effects of our lives upon others. The basic idea with (1) is that your current self is not the only iteration of you that will exist. In the future, things might be very different, many people miserable today are happy and virtuous later in life. Moreover, our later selves are dependent upon the survival of our current selves. That dependency matters--which brings me to (2). With (2) the important bit is to realize that our lives affect others, and our deaths affect others. Our children, friends, parents, students, those who benefit from our work, etc. Those effects upon others are morally significant, even if we don't choose them or choose those relationships ("I didn't choose to be your child," is no basis for refusing the obligations of children to parents). I think it's a mistake to ground moral obligation entirely upon choice, agreement, or consent ("I'm only obligated if I've chosen to or agreed to be"), in part because that implies that there can be nothing problematic in retracting or not giving consent ("If I choose not to go on living, that's my choice"). I think there are circumstances where it's wrong not to acknowledge obligations to which we did not consent. Our obligations are better understood, I think, as being grounded in our recognition of the good of certain practices and ways of being rather in our having chosen them. You will have noticed that my scheme does allow for suicide in cases where (1) there are no future selves (perhaps because of terminal disease) and where no one depends upon the person contemplating suicide and no bad consequences to others will result. I also accept that enormous and untreatable pain can provide grounds for suicide, and I accept that there may be cases where a suicide can be permitted because the consequences for others is good (e.g. in a case where someone sacrifices his or her own life to save others).

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