We first establish the point of the story:
| 1 | If some defensible ethical theory is true, then it is morally right for you to disconnect yourself from the famous violinist. | ||
| 2 | Some defensible ethical theory is true. | ||
| Therefore | 3 | It is morally right for you to disconnect yourself from the famous violinist. | 1&2 |
Next, we spell out the rest of the abortion argument:
| 1 | No fetus may be killed. | ||
| 2 | If no fetus may be killed, then it is not morally right for a woman to abort a pregnancy due to rape. | ||
| Therefore | 3 | It is not morally right for a woman to abort a pregnancy due to rape. | 1&2 |
But now we have the analogical argument:
| 1 | PA : If one of any two actions which are similar in all morally relevant respects is morally right, then so is the other, and if one of any two actions which are similar in all morally relevant respects is morally wrong, then so is the other. | ||
| 2 | Disconnecting yourself from the famous violinist and a woman's aborting a pregnancy due to rape are similar in all morally relevant respects. | ||
| 3 | It is morally right for you to disconnect yourself from the famous violinist. | ||
| Therefore | 4 | It is morally right for a woman to abort a pregnancy due to rape. | 1,2&3 |
So now we have a valid argument with a false conclusion:
| Step 1: | 1 | Every fetus is a person. | |
| 2 | Every person has a right to life. | ||
| Therefore | 3 | Every fetus has a right to life. | 1&2 |
| Step 2: | 4 | A fetus' right to life is more stringent than a mother's right to determine what happens in and to her body. | |
| 5 | If a fetus' right to life is more stringent than a mother's right to determine what happens in and to her body, then no fetus may be killed. | ||
| Therefore | 6 | No fetus may be killed | 4&5 |
| Step 3: | 7 | If no fetus may be killed, then it is not morally right for a woman to abort a pregnancy due to rape. | |
| Therefore | 8 | It is not morally right for a woman to abort a pregnancy due to rape. | 1&7 |
We have agreed to accept the truth of premise (1) for the sake of argument. Premise (2) is undeniably true, as are premises (5) and (7). Now recall our all too brief logic lesson. If we have a valid argument with a false conclusion, at least one of the premisses must be false. But all the premisses except premise (4) are either clearly true or granted to be true for the sake of argument. It follows that premise (4) must be false. That is to say, it is false that a fetus' right to life is more stringent than a mother's right to determine what happens in and to her body. As Thomson puts the point, "something really is wrong with that plausible-sounding argument I mentioned a moment ago."
In order for Thomson's argument to work, however, it must be the case that disconnecting yourself from the famous violinist and a woman's aborting a pregnancy due to rape are similar in all morally relevant respects. Let us compare the two:
How they are alike:
| The act of disconnecting yourself from the famous violinist. | The act of a woman's aborting a pregnancy due to rape. |
| Kidnapping is morally wrong. | Rape is morally wrong. |
| The hospital stay would last nine months. | The pregnancy would last nine months. |
| The violinist is an innocent human being. | The fetus is an innocent human being. |
| Disconnecting from the violinist amounts to killing the violinist. | Aborting the pregnancy amounts to killing the fetus. |
How they differ:
| The act of disconnecting yourself from the famous violinist. | The act of a woman's aborting a pregnancy due to rape. |
| The famous violinist is famous and can play the violin. | The fetus is neither famous nor can it play the violin. |
| You may not be female. | The woman is female. |
| You cannot leave the hospital and so do not have freedom of movement. | The woman has, for the most part, freedom of movement. |
| Disconnecting from the violinist is merely refusing to save. | Aborting the pregnancy is actively killing the fetus. |
It seems, then, that the two actions are similar in all morally relevant respects.