The impairment argument, ethics of abortion, and nature of impairing to the n + 1 degree.

I argue here that the impairment principle requires clarification. It needs to explain what makes one impairment greater than another, otherwise we will be unable to make the comparisons it requires, the ones that enable us to determine whether b really is a greater impairment than a, and as a result, whether causing b is immoral because causing a is. I then develop two of what I think are the most natural accounts of what might make one impairment greater than another. The quantitative understanding of greater impairment is problematic because it leaves the impairment principle vulnerable to counterexamples; just because impairment b impairs a larger number of abilities or the same number of abilities but for a longer period or to a higher degree does not mean that b is a greater impairment than a. The qualitative understanding of greater impairment is problematic because it does not explain examples of greater impairment used in the literature, means that an abortion is always a qualitatively more severe impairment than causing fetal alcohol syndrome regardless of how the organism is affected, and/or entails that lethal impairment is always greater than nonlethal impairment.