Philip Pettit’s republican conception of freedom is presented as an alternative both to negative and positive conceptions of freedom. The basic idea is to conceptualize freedom as non-domination, not as non-interference or self-mastery. When compared to negative freedom, Pettit’s republican conception comprises two controversial claims: the claim that we are unfree if we are dominated without actual interference, and the claim that we are free if we face interference without domination. Because the slave is a widely accepted paradigm of the (...) unfree person, the case of a slave with a non-interfering master is often cited as providing a good argument for the first republican claim and against a negative conception of freedom. One aim of this article is to raise doubts about whether this is true. The other aim of the article is to show that the prisoner—also a paradigm of the unfree person—presents a good argument against the second republican claim and in favour of a negative conception of freedom. This is called the ‘prisoner-argument’. It will be argued that neither Pettit’s distinction between free persons and free choices nor his distinction between compromising and conditioning factors of freedom can help to rebut the charge of the prisoner-argument. (shrink)