PhilosophersGiordano Bruno

Giordano Bruno

The universe is infinite, filled with countless worlds.

Humanism · Neoplatonism1548 – 1600 ItalyPhilosopher of natureCosmologist of the infinite universeFormer Dominican, condemned for heresyWriter of dialogues
On the Infinite Universe and Worlds, dial. I (1584); 1592 deposition

An infinite cause, an infinite universe

What it claims

The universe is infinite and contains innumerable worlds: it is the infinite image of God's infinite power.

Why

An infinite power produces everything possible, and in God power and action are one: so the universe is infinite.

Valid with an implicit premise

Bruno is not trying here to prove that God exists: he assumes it, as his opponents do. He asks what follows from a God of infinite power. His answer: such a God cannot have settled for a small world closed in by spheres. The universe must be infinite, filled with an infinity of worlds, like an infinite image of God. He summarised this himself before his judges in 1592. We file the argument under pantheism because it makes the world the necessary expression of God, a God who does not choose and cannot do otherwise. But Bruno still distinguishes God's infinity from the universe's: today one would rather say "panentheism" (everything is in God, God exceeds the world), a camp that does not exist on this site.

P1God, the first cause, has infinite power. (The theologians he opposes grant this too.)
P2An infinite universe, with innumerable worlds, is possible: the space beyond our world can receive another world, and others again, without end. And each of these worlds would be as good as ours.
P3 · implicit premiseAn infinite power can produce whatever is possible.
P4In God, being able and doing are one and the same: he cannot do other than he does. So what he can do, he does. Otherwise his power would remain "idle", as if grudging to give itself.
Therefore the universe is infinite and contains innumerable worlds: it is the infinite image of God's infinite power.

click a premise to reject it

If you accept every premise, logic forces you to accept the conclusion. So the debate is about the premises.
Checked by a logic solver: the premises cannot all be true while the conclusion is false.
Without the implicit premise: Without P3, the computer finds a case where God has infinite power, an infinite universe is possible, and God does all he can, but where that infinite universe is not among the things he can do: then the world remains finite.
Valid with P3. Bruno does not write it, because for him it is almost the definition of infinite power. But that is where the whole question lies: for Aristotle, God is infinite only in a certain sense, and an infinite body is not possible at all (which challenges P2). The premise most disputed by theologians is P4: if God necessarily does all he can, he did not create the world freely. Bruno knows it: he judges his reasoning demonstrative, but approves of theologians who do not teach it to the people.
Analogy. Imagine a painter of infinite talent who, given the choice, painted only a miniature in one corner of the canvas and left the rest blank. For Bruno, that would be the very image of wasted power. An infinite God must fill the infinite. The image is not his; he speaks of a boundless "mirror" in which the divine image must shine.

Objections

5

Each objection is a conversation: click to see who replies and where the debate stands.

Aristotle 340 BC · attacks premise 2

An infinite body is impossible. Every sensible body is heavy or light, so it has a natural place, an up and a down, a centre toward which it tends. An infinite body would have no centre, no up, no down: one cannot say both that there is an infinite body and that bodies have a place.

Bruno replies
Bruno
In his dedicatory letter, Bruno announces that his dialogues show that an infinite body is neither heavy nor light, and in which cases a finite body takes on these differences; Aristotle's arguments assume a centre and a circumference, that is, what is in question.
The debate goes on (our summary) Bruno separates weight from the idea of a centre of the world: only parts detached from their star "fall" toward it. Newton, a century later, would give a quite different theory: weight becomes an attraction between all bodies, with no natural place and no centre of the world toward which everything falls.
Thomas Aquinas 1266 · attacks premise 2

A natural body cannot be actually infinite: every natural thing has a determinate form, hence a determinate size. Likewise an actually infinite multitude is impossible, since every number is measured. The infinite exists only as the possibility of adding or dividing without end, never as a finished thing.

Bruno replies
Bruno
To the Aristotelian argument that there is no actual infinite and that no determinate number of worlds is more reasonable than another, Bruno answers that one can conclude from it, and even more easily, that the number of worlds is not determined but infinite.
The debate goes on (our summary) The reply turns the argument around but does not refute its principle (no completed infinite). The question of the actual infinite remained debated until Cantor, at the end of the 19th century, made it a mathematical object.
Thomas Aquinas and the theologians 1268 · attacks premise 4

God does not create by necessity of nature but by free will. His infinite power does not oblige him to do everything: he can do other than he does, and no creature, even an infinite one, would add anything to his goodness. A finite world is therefore no sign of a "grudging" or "idle" power (Summa theologiae I, q. 19, a. 3 and q. 25, a. 5; these questions are not yet in our corpus).

Bruno replies
summary: their text is not yet in our corpus
Bruno Filoteo, Bruno's spokesman
Filoteo holds demonstrative the reasoning that concludes God cannot do other than he does; yet he praises the theologians who do not accept it, because the people, persuaded of this necessity, would no longer understand choice, merit and justice.
The debate goes on (our summary) So Bruno does not refute the thesis of divine freedom: he excuses it for moral and practical reasons. For the theologians this is precisely the admission of the problem: a God who cannot do otherwise is no longer the creator God who chooses.
J
Johannes Kepler 1606 · attacks the conclusion

Nothing in observation shows an infinite universe: the region of the fixed stars does not resemble the Sun's, and our world seems to have a special place. Kepler also admits that such a thought carries "I know not what secret horror": one finds oneself wandering in an immensity without bounds or centre (On the New Star, 1606, ch. 21; text not collected).

no reply
summary: their text is not yet in our corpus
No reply possible: objection raised in 1606, after the author's death (1600).
The debate goes on (our summary) Modern astronomy has proved Bruno right on one point (stars are suns, many have planets) and leaves the other open: we do not know whether the universe is spatially infinite.
Kant 1781 · attacks premise 2

Reason can prove just as well that the world is finite in space and that it is infinite: this is the first "antinomy". The two proofs are equally strong, which shows that the question exceeds what we can know. Reasoning about the universe as a completed whole, finite or infinite, takes us beyond possible experience (Critique of Pure Reason; this passage is not yet in our corpus).

no reply
summary: their text is not yet in our corpus
No reply possible: objection raised in 1781, after the author's death (1600).