clearstream
(He, Him)
That's a helpful definition and pair of examples to have, and I can preface what I will add with a confession that I see the line between principles and rules as irreparably permeable... not found in any fixed place. With that said...In philosophy of law, the contrast between rules and principles is sometimes (maybe "often" would be better) understood as being between being amenable to all or nothing application (rules are like this) vs having weight but not, in themselves, being determinative (principles are like this).
An example of a rule: do not drive faster than the marked speed limit.
An example of a principle: those who create risk should bear the cost of harm that results from that risk crystallising.
In games, rules seem like basic tools of play. They typically exert an effect upon players (procedural rules) or game state (mediating rules) at such moments as circumstances prompt and justify invoking them. As your definition lays out, often they have their all-or-nothing effect and then fall silent again. Players use rules to constitute and enact their playful intentions. A rule can feel external to them: they follow its instructions and do the thing, but so could another.
But what playful intentions are the right sort? That is defined by principles, which outline ideal behaviour. They typically exert their effect upon players; not in a transient all-or-nothing way, but as a constant conditioning while within the magic circle. Players accept principles to use rules as intended and avoid using them not as intended. They must internalise principles, forming intentions of their own in accord with them.
I see that as connected with the notion that agreement to a rule is not found in that rule. Implying that in some sense all rules must be complexes or control-surfaces wrapping other things. Principles are good candidates for such "other things."Some legal requirements can be stated with the syntax of a rule - eg a person who causes harm by negligent action, to someone to whom they owe a duty of care, will be liable to compensate that harm - but may be better analysed as complexes of principle (eg the negligence "rule" combines the principle I stated just above, with other principles about remoteness, foreseeability, community and professional standards and expectations, etc).
An illustrative example is the "PERSUADE (vs PCs)" move in Stonetop. Taken literally with no regard for principles, it is exploitable as an XP pump. One thing at stake is seeing that rules have the result on play that their designer intended.I'm not sure what's at stake, in the context of RPG design and play, in the distinction between rules and principles. In Apocalypse World, a distinction is drawn between principles and moves. Player-side moves are particular mechanical "widgets" and processes that either affect other moves, or else mediate changes in the fiction (as per Vincent Baker's work on clouds and boxes). GM-side moves are particular patterns of fiction-introduction, that help discipline and direct the GM's introduction of fiction.
I perceive a virtuous layering effect that has utility to designers, which is that the conditioning by shared principles can lead to more apt, accurate and forceful employment of the rules.I don't see what utility there is in denying that the AW principles are not rules. They set normative standards for the GM to comply with. Sometimes they might need to be "balanced" or "weighed" against one another - eg Look through crosshairs and Be a fan of the players' characters might sometimes come into tension (suppose a NPC is very precious to a PC) - but this is not true of all of them. Make your move, but never speak its name and Make your move, but misdirect, are particularly clear examples here: there is no reason that the GM should not comply with these in every moment of play.
Having constructed a ruleset, designer can observe playtests and figure out which principles will most accurately and powerfully drive the use of the rules that they intend. Consciously laying out the conditions within which their rules will thrive. (Albeit, as @Manbearcat observes, that's still rather a work in progress for the field overall.)