GALILEO GALILEI

Facts which at first seem improbable will, even on scant explanation, drop the cloak which has hidden them and stand forth in naked and simple beauty.

We cannot teach people anything; we can only help them discover it within themselves.

Nature is relentless and unchangeable, and it is indifferent as to whether its hidden reasons and actions are understandable to man or not.

And yet it moves.

I have never met a man so ignorant that I couldn't learn something from him.

Measure what is measurable, and make measurable what is not so.

The sun, with all those planets revolving around it and dependent on it, can still ripen a bunch of grapes as if it had nothing else in the universe to do.

We must say that there are as many squares as there are numbers.

It is surely harmful to souls to make it a heresy to believe what is proved.

I think that in the discussion of natural problems we ought to begin not with the Scriptures, but with experiments, and demonstrations.

The Bible shows the way to go to heaven, not the way the heavens go.

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual.

It vexes me when they would constrain science by the authority of the Scriptures, and yet do not consider themselves bound to answer reason and experiment.

Where the senses fail us, reason must step in.

By denying scientific principles, one may maintain any paradox.

The Milky Way is nothing else but a mass of innumerable stars planted together in clusters.

If I were again beginning my studies, I would follow the advice of Plato and start with mathematics.

And who can doubt that it will lead to the worst disorders when minds created free by God are compelled to submit slavishly to an outside will? When we are told to deny our senses and subject them to the whim of others? When people devoid of whatsoever competence are made judges over experts and are granted authority to treat them as they please? These are the novelties which are apt to bring about the ruin of commonwealths and the subversion of the state.

I do not feel obliged to believe that the same God who has endowed us with senses, reason and intellect has intended us to forego their use and by some other means to give us knowledge which we can attain by them.

All truths are easy to understand once they are discovered; the point is to discover them

I have been enjoined by this Holy Office altogether to abandon the false opinion which maintains that the sun is the center and immovable, and forbidden to hold, defend, or teach the said false doctrine in any manner, and after it hath been signified to me that the said doctrine is repugnant with the Holy Scripture, I have written and printed a book, in which I treat of the same doctrine now condemned, and adduce reasons with great force in support of the same, without giving any solution, and therefore have been judged grievously suspected of heresy; that is to say, that I held and believed that the sun is the center of the universe and is immovable, and that the earth is not the center and is movable; willing, therefore, to remove from the minds of your Eminences, and of every Catholic Christian, this vehement suspicion rightfully entertained toward me, with a sincere heart and unfeigned faith, I abjure, curse, and detest the said errors and heresies, and generally every other error and sect contrary to Holy Church; and I swear that I will never more in future say or assert anything verbally, or in writing, which may give rise to a similar suspicion of me; but if I shall know any heretic, or anyone suspected of heresy, that I will denounce him to this Holy Office, or to the Inquisitor or Ordinary of the place where I may be; I swear, moreover, and promise, that I will fulfill and observe fully, all the penances which have been or shall be laid on me by this Holy Office.

I would beg the wise and learned fathers (of the church) to consider with all diligence the difference which exists between matters of mere opinion and matters of demonstration. ... [I]t is not in the power of professors of the demonstrative sciences to alter their opinions at will, so as to be now of one way of thinking and now of another. ... Demonstrated conclusions about things in nature of the heavens, do not admit of being altered with the same ease as opinions to what is permissible or not, under a contract, mortgage, or bill of exchange.

Who would set a limit to the mind of man? Who would dare assert that we know all there is to be known?

Philosophy is written in this grand book, the universe, which stands continually open to our gaze. But the book cannot be understood unless one first learns to comprehend the language and read the letters in which it is composed.

I give infinite thanks to God, who has been pleased to make me the first observer of marvelous things.