In section 23 of his 2d Treatise on Government: “On Civil Government” (in Chapter IV "Of Slavery"), John Locke makes what I consider two logical errors. Taking as given the religious condemnation of suicide in his cultural milieu, he argues:
Since I do not have the right to kill myself, I also cannot give someone else the right to kill me.
Since freedom is so crucial to the preservation of my life, I also cannot give away my own freedom.
However, John Locke also suggests
If I commit a crime worthy of death, that the individual or group I have harmed can choose to commute a sentence of death to a sentence of slavery.
Being enslaved is no worse a punishment that death because, as a practical matter, it is very difficult to prevent me from killing myself if I viewed slavery as worse.
Here is the exact text:
This freedom from absolute, arbitrary power, is so necessary to, and closely joined with a man’s preservation, that he cannot part with it, but by what forfeits his preservation and life together: for a man, not having the power of his own life, cannot, by compact, or his own consent, enslave himself to any one, nor put himself under the absolute, arbitrary power of another, to take away his life, when he pleases. No body can give more power than he has himself; and he that cannot take away his own life, cannot give another power over it. Indeed, having by his fault forfeited his own life, by some act that deserves death; he, to whom he has forfeited it, may (when he has him in his power) delay to take it, and make use of him to his service, and he does him no injury by it: for, whenever he finds the hardship of his slavery outweigh the value of his life, it is in his power, by resisting the will of his master, to draw on himself the death he desires.
The lesser of the two logical problems is that John Locke effectively allows me to give away my freedom by committing a serious crime. So I can give away my freedom by committing a serious crime. John Locke could answer that since I do not have the right to commit the crime, I also do not have the right to give away my freedom in this way. And few people are eager to give away their freedom, so allowing such a loophole for giving away one's freedom is unlikely to be a practical problem. The usual temptations to give away one's freedom involve selling one's freedom in some way for something else one wants. And the usual temptations for crime are the hope of getting something one wants from the crime without losing one's freedom or suffering any other penalty.
The bigger logical disjunction here is that for some reason, John Locke regards suicide as an alternative to slavery as a legitimate choice, while suicide under other circumstances is not. But if suicide as an alternative to slavery is legitimate, why wouldn't suicide as an alternative to an extraordinarily painful and lingering terminal disease be legitimate? (Suppose everyone agreed that enduring the extraordinarily painful and lingering terminal disease was worse than enduring slavery.) Or if it is illegitimate to commit suicide as an alternative to suffering under an extraordinarily painful and lingering terminal disease, shouldn't suicide as an alternative to a situation of bondage more bearable than that disease also be illegitimate?
For links to other John Locke posts, see these John Locke aggregator posts: