Meaning of "Of which the first ne'er knows the second cause" in Byron's Don Juan

Question

From Byron's Don Juan:

Their poet, a sad trimmer, but no less
In company a very pleasant fellow,
Had been the favourite of full many a mess
Of men, and made them speeches when half mellow;
And though his meaning they could rarely guess,
Yet still they deign'd to hiccup or to bellow
The glorious meed of popular applause,
Of which the first ne'er knows the second cause.

What is the meaning of the line in bold? What is the first cause and what is the second cause? How can a cause know another cause?

Answer 1

@Bellerophon gets the interpretation right in the comments.

The last line refers to the "first cause" and the "second cause" of the applause. The last lines read

The glorious meed of popular applause,
Of which the first ne'er knows the second cause.

Because the line says "the second cause", the phrase "the first" must refer to a "first cause". And the "of which" indicates that these two causes must be causes of the applause.

The first (and proximate) cause is the poet's speech, or by metonymy, the poet himself, but the second cause is the fact that the audience (like the poet¹) is drunk—one can deduce that the audience is drunk because they are hiccuping. Thus, they are applauding the poet's rambling and incoherent speech, even though they might not if they were sober. And the poet never realizes that his speech is incoherent, because he is being applauded nonetheless.

¹ _{mellow used to mean drunk.}

Answer 2

The first cause is a philosophical notion that goes back to Aristotle. It means, roughly, the originating agent of all phenomena. Aristotle called this ὃ οὐ κινούμενον κινεῖ, ho ou kinoúmenon kineî, or "that which moves without itself being moved." The scholastic Thomas Aquinas identified this "prime mover" with the Christian God. Following Aristotle, Aquinas argued that each phenomenon has a cause; that cause itself has another cause, and so on back through a causal chain to the first cause, which is the causeless or self-caused God. The term "first cause" for God is common in Christian theology and philosophy; the Oxford English Dictionary quotes Gower's Confessio Amantis vol. III. 87:

He clepeth god the firste cause.

_{“Cause, N., Sense I.5.” Oxford English Dictionary, Oxford UP, July 2023, https://doi.org/10.1093/OED/3240575751. clepeth means calls.}

There is AFAIK no philosophical or Christian notion of a second cause. Byron is postulating one tongue-in-cheek to claim that the causal chain for the applause cannot be divined back to the first cause. He is saying that even the first cause does not know the second cause for this applause. That is to say, let alone the drunken listeners themselves, even God has no idea why they are applauding.