The idea that science is "value free" can be traced back to the emergence of the distinction between fact and value in the 17th century. It can be considered to have three components: impartiality, neutrality and autonomy. We show that important parts of these component ideas were developed and defended by Galileo, principally in his letters to Castelli and to Grand Duchess Cristina and in his books The Assayer and Two Chief World Systems. Galileo's argument for autonomy is particularly powerful and, although lacking the generality introduced in later arguments (since his principal concern was to win autonomy for science from the authority of the Church), it remains at the core of all subsequent defenses of the autonomy of science. This argument is based on three suppositions: that scientific understanding is subject to criteria that are independent of the Church's authority and of any value perspective, that scientists have cultivated the virtues of the "scientific ethos", and that (because they use different languages - the "two books" argument) there cannot be contradiction between properly made scientific judgments and declarations of the Church. Finally some limitations of Galileo's arguments are indicated but not developed.