Upvoted, but even with communication beforehand, the rational move in a one-shot PD is to defect.
Taboo "rational".
Unless there is some way to make binding commitments, or unless there is some kind of weird acausal influence connecting the players.
Acausal control is not something additional, it's structure that already exists in a system if you know where to look for it. And typically, it's everywhere, to some extent.
Taboo "rational".
Highest-scoring move, adjective applied to the course that maximises fulfillment of desires.
The best move in a one-shot PD is to defect against a cooperator.
With no communication or precommitment, and with the knowledge that it is a one-shot PD, the overwhelming outcome is both defect. Adding communication to the mix creates a non-zero chance you can convince your opponent to cooperate - which increases the utility of defecting.
A monthly thread for posting rationality-related quotes you've seen recently (or had stored in your quotesfile for ages).