Experiment

The extent to which Galileo did experiments has been a controversial issue. The dominant view well into the twentieth century was that Galileo was among the first "scientists" who experimented extensively and developed his theories on the basis of his experiments. In the 1930s Alexandre Koyré disputed that view and argued strenuously that Galileo's engagement with experiment was minimal. Galileo, according to Koyré, was a Platonist philosopher, who, for the most part, did not perform real experiments and reached his theoretical conclusions relying on a priori (deductive) reasoning and thought experiments. A significant reason for Koyré's claim was the excessive accuracy of many of the experimental results that Galileo reported in his published work.

Subsequent scholars have disputed some of Koyré's claims. Starting in the early 1960s, Thomas B. Settle and Stillman Drake, among others, drawing on a wider range of Galileo's manuscripts than was available to Koyré, managed to replicate several of Galileo's experiments on motion and obtained results that were close to the ones that he reported. In the wake of these studies, a consensus has developed among Galileo scholars that he was an ingenious experimenter, who designed and carried out a variety of experiments. Furthermore, experimentation and measurement were essential to Galileo's widely known discoveries, the law of free fall and the parabolic trajectories of projectiles. Galileo's image as the preeminent experimental philosopher has been reinstated.

One of the problems faced by experimental philosophers was how to legitimize experimentation as a means of acquiring knowledge of nature. Common experience could function as an unproblematic foundation for natural philosophy because of its familiarity and accessibility to everyone. The novel phenomena discovered by means of experiment, on the other hand, were neither familiar nor accessible to all. Two issues had to be tackled: first, the veracity of experimental results had to be attested. Second, particular results obtained under local, contingent circumstances had to acquire the status of general truths about nature.

An instance of how Galileo attempted to address these issues is provided by his investigations of free fall, which were carried out in the early years of the seventeenth century and published many years later in his Two New Sciences (1638). In that work he did not provide any circumstantial information about the particular experiments he had performed with rolling balls on incline planes. Furthermore, he did not report the specific results he had obtained. Rather he gave a generic description of the experimental setup and pointed out that the results conformed repeatedly ("a full hundred times") to what he had anticipated.

Experimental philosophers in the Baconian tradition also faced the problem of legitimizing experiment, but they confronted it differently. This tradition is the topic of the next two sections.