Response to Thomson's violinist example:

Abortion isn't permissible unless the woman was raped.

Principle: If you voluntarily act in a way that brings about the existence of a person, then you have a responsibility to maintain the life of that person. That person has a right to whatever you can provide it to sustain its life.

Counter-example: People seeds

Warren's criticism of Thomson:

Principle: If you voluntarily, knowingly, get into a situation where a person with full moral rights is dependent upon you for his/her continued existence, then it would be wrong to refuse to do what is necessary to keep that person alive.