Introduction to
"Dialogue about the two greatest world systems"

Galileo Galilei
- 1632 -

To the moderate Reader

Few years ago, it was promulgated in Rome a salutary edict, which, in order to obviate the dangerous scandals of the present age, imposed an opportune silence to the Pythagorean opinion about the mobility of the Earth. There was someone who rashly affirmed that decree wasn't the result of a judicious examination, but of a little informed passion, and there was someone who complained that some persons totally inexpert in astronomic observations had not to clip speculative minds' wings. Hearing the temerity of such complaints, my zeal wasn't able to keep silent. Since I was completely informed about that prudent determination, I thought to appear in the theater of the world, as witness of sincere truth. I was then present in Rome: I had not only hearings, but also applauses of the most eminent prelates of that Court; and after I was informed, than there was the publication of that decree. In the present work, therefore, I want to show to the foreign nations, that about this subject we know in Italy, and particularly in Rome, more than any imagination of the ultramontane diligence; and picking up all the speculations about the Copernican system, I intend to let know that the Roman censorship examined them, and that out of this climate come not only the dogmas for the soul health, but also some clever expedients to delight the talents.

Therefore, in the discourse I have supported the Copernican part, proceeding in pure mathematical hypothesis, looking for every way to represent it superior, not to that of the steadiness of the Earth absolutely, but to that defended by some Peripatetics, but only in name and not in fact, because they are happy, without walking, to adore the shades, not philosophizing with the proper prudence, but with the memory of four misunderstood principles.

Three principal items will be treated. First of all I'll try to show that all the feasible experiences on the Earth are inadequate to deduce its mobility, but they are indifferently able to be adapted both to the mobile Earth and to the quiescent Earth; and I hope that in this case a lot of unknown observations to the antiquity will be revealed. Secondly the celestial phenomenons will be examined, strengthening the Copernican hypothesis as if it would be absolutely victorious, adding new speculations, which however serve for facility of astronomy, not for necessity of nature. Thirdly I will propose a clever imagination. Many years ago, I said that the unknown problem of the flow of the sea would be solved, if we admitted the terrestrial motion. This sentence of mine, flying among the men's mouths, found charitable fathers who adopted it as a result of their talent. Now, in order that any foreigner, strengthening with our weapons, could never appear and blame our little prudence in such principal accident, I have judged to reveal those probabilities that would make it persuasible, if the Earth moved. I hope that from these considerations the world will know, that if others nations have sailed more, we have not speculated less, and that affirming the steadiness of the Earth doesn't come from other people's thought, but from those reasons which are administered us by the pity, the religion, the knowledge of the divine omnipotence and the conscience of the weakness of the human talent.

I have thought, then, that it's suitable to explain these concepts in form of dialogue: in fact, it is not narrowed to the rigorous observance of the mathematical laws, and it lets some detours, which are sometimes not less curious than the principal matter.

Many years ago, in the wonderful city of Venice, I had some conversations with Mr. Giovan Francesco Sagredo, illustrious for birth, acute for talent. From Florence came there Mr. Filippo Salviati, in which the smallest shine was the clarity of the blood and the magnificence of the wealths; sublime intellect, which feeds itself with no delights more greedily than with exquisite speculations. I often discussed with these two men about those subjects, with the intervention of a peripatetic philosopher, to which it seemed that nothing hindered the intelligence of the true more than the fame acquired in the Aristotelian interpretations.

Now, since the sour death has deprived Venice and Florence of these two big lights, in their most beautiful years, I have resolved to prolong, as far as can my weak strength, their life's fame with these papers of mine, introducing them as interlocutors in the present controversy. And I'll give a place also to the good Peripatetic, who will be named Simplicio, because of his excessive affection toward the comments of this revered writer. I hope that those two great spirits, always venerable to my heart, appreciate this public monument of my never-ending love, and that they help me to explain to the posterity the promises speculations with the memory of their eloquence.

Among these Lords there were casually (as it happens) some discussions, which had more excited than appeased their learning thirst: therefore they made wise resolution to stay together for some days, in which, banished every other occupation, they attend to contemplate with more orderly speculations the wonderful of God in the sky and in the earth. Met together in the illustrious Sagredo's palace, after the due but brief compliments, Mr. Salviati began in this manner.

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