"Il Dialogo dei Massimi Sistemi"

Il sistema tolemaico

Cover of the "Dialogo"
A page of the "Dialogo"
The Dialogue, published in Florence with the ecclesiastic imprimatur after laborious negotiations with Rome and intended to defend Copernican theories with appropriate proofs, is a debate divided into four days among three characters created by Galileo's imagination, two of whom, Salviati and Sagredo, take after two living men. In the Dialogue Filippo Salviati (1583-1614) is the official defender of Copernican theses; Giovanfrancesco Sagredo (1571-1620) an educated liberal Venetian nobleman with a good willingness to accept new ideas is a sort of chairman between Salviati and the third invented character, Simplicio, a convinced Aristotelian.. The latter's name is a clear evidence of Galileo's strategy. In fact Simplicio was one of the most famous of Aristotle's commentators, but his name in Italian could also refer to simple mindedness. Later someone made Pope Urbano VIII° suspect that Simplicio was his caricature, which did not help Galileo
The scene of the Dialogue, is Sagredo palace in Venice. In the preface addressed to the discreet reader (it is important to observe that Galileo used a modern style which, together with the use of Italian, is evidence of a way of communicating which was much easier than the
one used in the traditional academic world), there is an argument already used in the letter to Ingoli: ’’…in this work it is my advice to show to foreign countries that
this subject is known in Italy and particularly in Rome as much as it is
carefully imagined beyond the mountains.
’’. It is an argument of national pride combined with a careful hint to the Pope's ideas: ’’…To start to affirm again that the Earth is motionless and to consider the opposite only as a mathematical freak does not arise because we don't know that others have thought of it but it comes from those reasons that mercy, religion, the aknowledgement of divine almightiness and the awareness of the weakness of the human mind give us.’’.

Even if a summary of the Dialogue is particularly difficult because of the wideness of the topic, the variety and the changeableness of the statements of the three partners, we can sum up the work briefly. The first day is basically dedicated to the radical challenge of
Aristotelian cosmology, in particular to the distinction between celestial and sublunar. In the second and in thethird day they try to prove the possibility of earth motions, resorting to the argument of the relativity of motion already developed in the answer to Ingoli, and trying to get round of the lack of direct proofs of the motion of the Earth. Finally the fourth day introduces the argument which according to Galileo is the most valid to prove the earth motion, that is the existence of tides. But what interests most is to stress the types of argumentations constantly used by Galileo. Even if the scientist often reproaches Simplicio for using retorical choice passages, at the same time he uses them when the opportunity turns up (see 'Science and Rhetoric' by Marcello Pera -ed.Laterza).
Two examples are enough:
Salviati often tries to cause problems to Simplicio, accusing him of disagreeing
with his own Aristotelic principles: Salviati-Doesn't (Aristotle) declare that what experience and sense demonstrate must be put before any other question even if it is well based? and doesn't he say it resolutely without hesitating at all?:’’. Simplicio-‘’He says so’’ . Salviati-‘’So of these two propositions which are both Aristotle's doctrine, the second which says that it is necessary to put sense to talk, is a much stronger doctrine than the other which considers the sky unalterable. But you will philosophize in a more Aristotelian way saying:<<The sky is unalterable because sense shows it to me>>, than saying:<<The sky is
unalterable because I am persuaded by Aristotle's doctrine>>
’’ (from the Dialogue 1).

Simplicio contests the possibility to apply the abstract concepts of mathematics to physical objects to which the exactitude of calculus does not suit, so Salviati replies from analogy: ’’Do you know Simplicio what happens? As an accountant tares crates and other things to equalize figures of sugars, silks and wools, in the same way a scientist who actually wants to recognize the effects abstractly proved must deduct the material reality from theory; if he can do that, I assure you that the effects will show up with fewer adjustments than calculations themselves’ (from the Dialogue 2).
The Dialogue, which is rich of an agile and easy way of communicating, as in the above argumentations, ends in a cleverly conciliatory way towards the doctrine of the Church. Simplicio aknowledges the cleverness of Salviati's talks about tides but he objects that God might have given origin to those phenomena even in ways which were inconceivable by human minds. ’’Wonderful and really angelic doctrine’’. And Sagredo adds:’’…And in the meanwhile we can, as usual, enjoy the cool air in the gondola which is waiting for us.’’
Go to Galileo