Premise: Abortion --> Killing of a Fetus

Premise: Fetus --> Person*

Premise: Fetus --> Innocent

Therfore:  Abortion --> Killing of an Innocent Person

Premise: Innocent Person --> Has a Right to Life

Therefore:  Abortion --> Killing of Something That Has a Right to Life

Crucial Premise: Killing of Something That Has a Right to Life --> Wrong

Therefore:  Abortion --> Wrong

*Granted for the Purpose of This Argument Only

Premise: A --> KF

Premise: F --> P*

Premise: F --> I

Therefore:  A --> KIP

PREMISE: IP --> HRTL

Therefore:  A --> KSTHRTL

CRUCIAL PREMISE: KSTHRTL --> W

Therefore:  A --> W

*Granted for the Purpose of This Argument Only

I. Either accept the conclusion or give up one or more of the premises

II. Thomson challenges the Crucial Premise:

Killing of Something That Has a Right to Life --> Wrong

The Crucial Premise is Incorrect. It should be replaced with:

Thomson's Substitute Premise:

UNJUST Killing of Something With a Right to Life --> Wrong

With the substitute premise, it does not follow that all abortions are wrong, but only abortions that involve unjust killings.

The Crucial Issue: For any particular abortion, we must ask whether it involves the unjust killing of a fetus.

Question: When does an abortion involve the unjust killing of a fetus?

Answer: When the fetus has a RIGHT to the use of the mother's body.

Crucial Distinction: RIGHTS (ENFORCEABLE Obligations) vs. UNENFORCEABLE OBLIGATIONS (e.g., the obligation to do the morally decent thing). Laws are only appropriate for ENFORCEABLE Obligations, not UNENFORCEABLE Obligations.

Thomson's Answer: If the mother has taken responsibility for the fetus or if she consents to the use of her body by the fetus, then the fetus has a right to the use of her body.

Only then does the woman have an OBLIGATION that may be ENFORCED by law.