mathematics, in order to prove his statement. In it bodies of different weights did not arrive at precisely the same time after having fallen from the tower, but the difference in time was slight. In spite of these differences and therefore really against the evidence of experience, Galileo upheld his proposition. The witnesses to this experiment, however, became really perplexed by the experiment and Galileo's upholding his view. They persisted the more obstinately in their former view. By reason of this experiment the opposition toward Galileo increased to such an extent that he had to give up his professorship and leave Pisa.

Both Galileo and his opponents saw the same "fact." But they interpreted the same fact differently and made the same happening visible to themselves in different ways. Indeed, what appeared for them as the essential fact and truth was something different. Both thought something along with the same appearance but they thought something different, not only about the single case, but fundamentally, regarding the essence of a body and the nature of its motion. What Galileo thought in advance about motion was the determination that the motion of every body is uniform and rectilinear, when every obstacle is excluded, but that it also changes uniformly when an equal force affects it. In his Discorsi, which appeared in 1638, Galileo said: "I think of a body thrown on a horizontal plane and every obstacle excluded. This results in what has been given a detailed account in another place, that the motion of the body over this plane would be uniform and perpetual if the plane were extended infinitely."

In this proposition, which may be considered the antecedent of the First Law of Newton, what we have been looking for is clearly expressed. Galileo says: Mobile . . . mente concipio omni secluso impedimento, "I think in my mind of something movable that is left entirely to itself." This "to think in the mind" is that giving oneself a cognition about a determination of things. It is a procedure of going ahead in advance, which Plato once characterized regarding μάθησις in the following way: ἀναλαβὼν αὐτὸς ἐξ αὑτοῦ

Martin Heidegger (GA 9) Modern Science, Metaphysics, and Mathematics - Basic Writings (1993)