QuestionsCan we be certain of anything?To deny causes is to deny reason
Can we be certain of anything?Yes, through reason

To deny causes is to deny reason

Averroes 1126 · 1198Truth cannot contradict truth: philosophy and faith agree.
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What it claims

Things have real natures and real causes: fire really is the cause of the burning. To deny causes is to deny reason, which is nothing other than the knowledge of things through their causes.

Why

Each thing has a nature from which its actions come; denying causes would destroy knowledge, and we do have certain science.

In short

"To deny causes is to deny reason" is an argument by Averroes (The Incoherence of the Incoherence, discussion 17 (c. 1180)) on the question "Can we be certain of anything?" (answer: yes, through reason). Its claim: Things have real natures and real causes: fire really is the cause of the burning. To deny causes is to deny reason, which is nothing other than the knowledge of things through their causes. According to AskPhilosophy's logic check (Z3 solver), the argument is valid only if one grants a premise the author leaves unstated (P3). AskPhilosophy presents 4 objections, 3 of them with a documented reply, and the original text behind each premise, checked word for word.

The Incoherence of the Incoherence, discussion 17 (c. 1180)
Valid with an implicit premise

Al-Ghazali had argued that the link between fire and burning is not necessary: it is God who creates the burning when the fire touches the cotton, and he could refrain from creating it (see his argument "Cotton and fire"). Some eighty-five years later, Averroes answers him sentence by sentence. For him, denying causes is not a theologian's daring: it is sawing off the branch on which all knowledge sits.

P1Each thing has its own nature, from which its own actions come: fire burns, water wets. A thing with no action of its own would have no nature of its own, and so neither name nor definition: we could no longer even say what it is.
P2Truly knowing a thing is knowing it through its definition and its causes. If things had neither definition nor causes, there would be neither science nor proof any more: only opinions.
P3 · implicit premiseWe do have true, certain science. Besides, saying that no knowledge is certain destroys itself: that sentence would not be certain either.
Therefore things have real natures and real causes: fire really is the cause of the burning. To deny causes is to deny reason, which is nothing other than the knowledge of things through their causes.

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 world with no causes, no definitions and no science: a world where nothing is really known. Nothing in P1 and P2 rules it out. That is the door a radical sceptic would choose; Averroes answers that this sceptic contradicts himself as soon as he asserts anything.
Valid if we add P3: we possess true science. Averroes does not state it as a premise; he takes it as evident and answers in advance whoever denies it: saying "no knowledge is certain" refutes itself. So the argument shows a price to pay: whoever denies causes must give up all science. It does not prove that fire always burns, and Averroes grants this: an obstacle (talc, it is said) can prevent fire from burning the cotton, without fire losing its nature of burning.
Analogy. Imagine a mechanic who said: "Nothing proves the engine turns the wheels; it's just that whenever it runs, the wheels turn too." He could no longer repair any car: repairing means looking for the cause of a breakdown. For Averroes, denying causes condemns us to understand nothing any more.

Objections

4

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

Al-Ghazali 1095 · attacks the conclusion

Observation only shows that the burning happens with the contact of fire, not that it happens by it. We never see the power of fire, only two events together. Nothing prevents it being God who creates the burning, directly, at the moment of contact.

Averroès replies
Averroès
Such a claim abolishes what our senses perceive of the existence of causes and effects. No philosopher doubts that fire is the cause of the cotton's burning. Not absolutely, he specifies: fire acts thanks to an external principle, which is a condition of the very existence of fire, let alone of its burning.
The debate goes on (our summary) The two men agree more than it seems: for Averroes too, fire is not enough on its own, it depends on a first principle. The disagreement is about the rest: for Averroes, God acts through the natures of things; for al-Ghazali, God acts directly, and the world's regularity is only a habit he keeps up.
Al-Ghazali (knowledge through habit) 1095 · attacks premise 2

We do not need necessary causes in order to know. What is repeated again and again is fixed in our minds by habit, and God creates in us the knowledge that he will not do the extraordinary things that remain possible. So our ordinary knowledge is safe, without necessary natures.

Averroès replies
Averroès
This is no real solution. The knowledge created in us always follows the nature of the real thing, for being right is believing that a thing is as it is. If we know what will happen, there must be, in the things or in their agent, a condition to which our knowledge refers: that is what the theologians call "habit". But God cannot have a habit. So this condition is in the things: it is what the philosophers call their nature.
The debate goes on (our summary) Al-Ghazali could answer that the nature of things depends at every moment on God, who can change it: indeed his second answer about fire accepts that fire has a nature (see his argument). The debate then turns on a finer point: does this nature bind God, or only us?
Al-Ghazali (miracles) 1095 · attacks the conclusion

If fire burns necessarily, by its nature, the miracle of the prophet Abraham thrown into the fire without burning becomes impossible. Yet a believer must accept it: God can change a property of the fire, or of the prophet's body.

Averroès replies
Averroès
The principles of religion, such as miracles, are divine realities that surpass human understanding: they must be acknowledged, even though their causes are unknown. That is why none of the ancient philosophers discussed miracles, although they were known everywhere.
Averroes 1180 · Later in the same discussion
The philosophers can grant that an agent does not always produce its effect, because of external things: it is not impossible that fire touches cotton without burning it, if something has been placed with the cotton that makes it non-inflammable, as is said of talc.
The debate goes on (our summary) The answer places miracles outside philosophy rather than explaining them, and talc is a natural obstacle, not a suspension of nature. And just before, he is harsh with those who discuss the principles of religion: in his view, heretics who deny them must be put to death. For a reader today, this is the limit of his freedom of thought.
Hume 1748 · attacks premise 1

We never see the power that would unite a cause to its effect: events seem conjoined to us, never connected. Our idea of cause comes from the habit of seeing things follow one another. So reason knows no "natures" that would necessarily produce their effects.

no reply
No reply possible: objection raised in 1748, after the author's death (1198).
The debate goes on (our summary) Hume does not deny causes as al-Ghazali does, and he does not appeal to God: he says reason cannot demonstrate them, but our nature forces us to believe in them. Averroes had answered a related idea in advance: if the "habit" is ours, it is just the normal activity of the intellect. But that is exactly what Hume disputes: that the intellect perceives the natures of things. The debate remains open: modern science speaks of laws discovered by experience, and many philosophers doubt that necessary natures can be drawn from them.