1. No necessary and sufficient conditions (though there are necessary conditions and there are sufficient conditions, they do not help resolve the abortion issue).

2. If fetus is a person, some abortions are permissible in self-defense against innocent threats to mother's well-being, life prospects, or mental or physical health. (This part of the argument follows Thomson.)

3. If fetus is not a person, coherence of our moral sentiments (e.g. sympathy) and attitudes would require that we give moral consideration to person-like beings. In the latest stages of pregnancy, abortion is psychologically akin to murder.

Like the other authors, Marquis does not rest his argument on the claim that the fetus is a person.

MAIN CLAIM: What makes the killing of an adult human being wrong is the loss of his or her future.

A fetus has a future (at least) as valuable as the future of an adult human being (i.e., a fetus has a future-like-ours).

Therefore, killing a fetus is (at least) as wrong as killing an adult human being.