"A moral conclusion about the goodness or evil of a human act is deduced from two premises: a major premise, which states a general moral principle (e.g. 'we ought to pay our debts') and a minor premise, which sees a particular situation as coming under that principle (e.g. 'international debts are debts'). Thus the essential pro-life argument is as follows. The major premise is: 'Thou shalt not kill' — i.e., all deliberate killing of innocent human beings is forbidden. The minor premise is that abortion is the deliberate killing of innocent human beings. The conclusion is that abortion is wrong."
-- Peter Kreeft