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 result 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 this place 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: "I think in my mind of something movable that is entirely left to itself." This "to think in the mind" (Sich-im-Geiste-denken) is that giving-oneself-a-cognition (Sich-selbst-eine-Kenntnis geben) about a determination of things. It is a procedure of going ahead in advance, which Plato once characterized regarding maqhsiV in the following way: "bringing up and taking up--above and beyond the other--taking the knowledge itself from out of himself." (Meno 85d)

There is a prior grasping together in this mente concipere of what should be uniformly determinative of each body as such, i.e., for being bodily. All bodies are alike. No motion is special. Every place is like every other, each moment like any other. Every force becomes determinable only by the change of motion which it causes--this change in motion being understood as a change of place. All determinations of bodies have one basic blueprint (Grundriss), according to which the natural process is nothing but the space-time determination of the motion of points of mass. This fundamental design of nature at the same time circumscribes its realm as everywhere uniform.

P. 90-91

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