Prudence for Aristotle was not at all a matter of timidity or self-protective conformity; and certainly it was not tainted with some notion of shop-keeperly stodginess. These are modern accretions, traceable to the Romantic Movement and Marxist politics. Pity the poor bourgeoisie, whom artists are always epatering for narrowness and penny-pinching and philosophers like Sartre are always accusing of bad faith.
The ancients saw Prudence as a sort of skillfulness in selecting the right means to obtain the right result. It might be a bit like what we call today a cost-benefit or risk-reward analysis of various courses of action in order to select the one that maximizes the latter term and minimizes the former one in each of these binaries. But even that is too mechanical a reading of it and leaves out the idea of the virtuous - conceived as a sort of power of the human spirit.
For Courage we can do no better than look to Plato himself, in an early dialogue called the “Laches”, so named after the Athenian General who is Socrates’s principal interlocutor in that dialogue. The General thinks that Courage is nothing more than putting one’s life on the line and charging in to battle on receiving provocation or for the sake of one’s honor or even to defend the polis: He is channeling the Homeric ethos. Socrates leads him gently to the conclusion that such actions have no independent value; they are not goods in themselves but must be done for the right ends and using the right means.
One might “marry” these two concepts, as Boyer says we should, and say that Courage needs to be informed by Prudence in order to be properly directed and that Prudence requires the spiritedness of Courage in order to be effective.
We moderns think we have made progress since those old guys thought about these things. Well, we have had other thoughts but they were not always better ones. A proper education ought to lead to rediscovery of these discarded pieces of wisdom. Better yet, that wisdom - and this was Boyer’s point - is especially needed in a time of crisis.