.synthetic a priori isn’t a principle, it’s a relation of the content of certain kinds of conceptions to each other — Mww

You said synthetic a priori is a principle; Kant says synthetic a priori judgements are principles. — Mww

Kant writes about synthetic a priori unity (B264), synthetic a priori concepts (A220), synthetic a priori about appearances (B217), synthetic a priori cognitions (B19) and synthetic a priori judgements (B19).

Paul Guyer and Allen Wood in the Introduction talk about synthetic a priori principles.

The "Transcendental Analytic" has prepared the way for this critique of traditional metaphysics and its foundations by its argument that synthetic a priori principles can be established only within the limited domain of sensible experience.

At this point in the Critique Kant has completed the largest part of his constructive project, showing how synthetic a priori principles of theoretical cognition are the necessary conditions of the application of the categories to sensible data structured by the pure forms of intuition.

Of course the synthetic a priori is a principle.

Kant writes about synthetic a priori unity (B264), synthetic a priori concepts (A220), synthetic a priori about appearances (B217), synthetic a priori cognitions (B19) and synthetic a priori judgements (B19). — RussellA

“….. the predicate B lies completely out of the conception A, although it stands in connection with it. (…) the latter add to our conceptions of the subject a predicate which was not contained in it (…) By the addition of such a predicate, therefore, it becomes a synthetical.…”

“…. Mathematical judgements are always synthetical…”
“…. proper mathematical propositions are always judgements à priori…”

“… Not only in judgements, however, but even in conceptions, is an à priori origin manifest….”

“…. The science of natural philosophy (physics) contains in itself synthetical judgements à priori, as principles….”

“…. I shall adduce two propositions. For instance, the proposition, “In all changes of the material world, the quantity of matter remains unchanged”; or, that, “In all communication of motion, action and reaction must always be equal.” In both of these, not only is the necessity, and therefore their origin à priori clear, but also that they are synthetical propositions. For in the conception of matter, I do not cogitate its permanency, but merely its presence in space, which it fills. I therefore really go out of and beyond the conception of matter, in order to think on to it something à priori, which I did not think in it. The proposition is therefore not analytical, but synthetical, and nevertheless conceived à priori; and so it is with regard to the other propositions of the pure part of natural philosophy…”

“…. metaphysics, according to the proper aim of the science, consists merely of synthetical propositions à priori….”
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Of course the synthetic a priori is a principle. — RussellA

Synthetic a priori is not itself a principle; it is the condition of principles, unities, conceptions and anything else to which it applies, in which representations relate to each other in a certain manner, re: synthetically, and, representations are of a certain origin, re: a priori.
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If you want to say certain forms of representations adhere to the synthetic a priori principle, you haven’t in the least said anything about those forms, other than give them a name, without anything about what it means to be so. So now you have to go back and describe what it means to adhere to such a principle, and you arrive at exactly where you should have began.

Ever notice…given that experience is knowledge, there is such a thing as synthetic a priori knowledge but no such thing as synthetic a priori experience?

Transcendental philosophy is rife with dualisms, and this is just another one of them.

’m inclined to suggest Bergson was Kantian, but the article doesn’t support me, so I better not. — Mww

Maybe it does. Consider this paragraph:

In Time and Free Will, Bergson argued that this procedure would not work for duration. For duration to be measured by a clock, the clock itself must have duration. It must exemplify the property it is supposed to measure. To examine the measurements involved in clock time, Bergson considers an oscillating pendulum, moving back and forth. At each moment, the pendulum occupies a different position in space, like the points on a line or the moving hands on a clockface. In the case of a clock, the current state – the current time – is what we call ‘now’. Each successive ‘now’ of the clock contains nothing of the past because each moment, each unit, is separate and distinct. But this is not how we experience time. Instead, we hold these separate moments together in our memory. We unify them. A physical clock measures a succession of moments, but only experiencing duration allows us to recognise these seemingly separate moments as a succession. Clocks don’t measure time; we do. This is why Bergson believed that clock time presupposes lived time.

This provides a connection between Bergson's concept of 'lived time' (or duration) and Kant’s idea of time as a form of intuition—a foundational structure through which we experience and organize reality. Bergson's critique aligns with Kant in suggesting that time is not merely a succession of isolated moments that can be objectively measured, but a continuous and subjective flow that we actively synthesize through consciousness. This synthesis is what lets us experience time as duration, not just as sequential units.

In this account, Bergson is challenging Einstein’s emphasis on clock-based measurement, pointing to the irreducibility of subjective experience in understanding time’s nature. Kant’s notion of time as an a priori intuition parallels this because he saw time as essential to organizing our experiences into coherent sequences. It’s not a feature of objects themselves but rather of our way of perceiving them—a precondition that shapes experience.

This is connected to why I argue for the 'primacy of perspective'. Without an observing mind that strings things together, there is no time as such. And despite Einstein's undoubted genius, he could never let go his realist convictions. I see that as a philosophical shortcoming.

Bergson's critique aligns with Kant in suggesting that time is not merely a succession of isolated moments that can be objectively measured, but a continuous and subjective flow that we actively synthesize through consciousness. — Wayfarer

Do you think it appropriate that we denote the succession of isolated moments as change, leaving time itself to represent continuous and subjective flow, which we think of as motion?
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Your primacy of perspective should be considered Philosophy 101.

I think so too but there doesn’t seem much awareness of it, let alone consensus.

As for the relationship of time and motion, that seems obviously implied by the equation of space and time in relativity. But neither space nor time are self-existent, so to speak.

Synthetic a priori is not itself a principle; it is the condition of principles, unities, conceptions and anything else to which it applies, in which representations relate to each other in a certain manner, re: synthetically, and, representations are of a certain origin, re: a priori................If you want to say certain forms of representations adhere to the synthetic a priori principle, you haven’t in the least said anything about those forms, other than give them a name, without anything about what it means to be so. — Mww

The relation between thought (a priori) and being (synthetic)

Paul Guyer and Allen Wood in the Introduction to CPR explicitly say that synthetic a priori principles can be established, meaning that there can exist synthetic a priori principles.

The "Transcendental Analytic" has prepared the way for this critique of traditional metaphysics and its foundations by its argument that synthetic a priori principles can be established only within the limited domain of sensible experience.

Yes, "synthetic a priori" is the name of a principle, not a description, in the same way that "the conservation of energy" and "the conservation of momentum" are names of principles.

Kant's "synthetic a priori" is the name of a principle that relates the synthetic to the a priori.

My original point is that B276 can be read as a transcendental argument, not in the sense of transcendental used by Kant in CPR A2, but in the sense as used by the Britannica.

CPR A2: "I call all cognition transcendental that is occupied not so much with objects but rather with our a priori concepts of objects in general. A system of such concepts would be called transcendental philosophy."
Britannica transcendental argument: "a form of argument that is supposed to proceed from a fact to the necessary conditions of its possibility."

In B276, The Refutation of Idealism, are the two statements which come under the Britannica definition of transcendental rather than the A2 definition.
1) The mere, but empirically determined, consciousness of my own existence proves the existence of objects in space outside me.
2) Consequently, the determination of my existence in time is possible only by means of the existence of actual things that I perceive outside myself.

This is why I originally proposed that “Kant's synthetic a priori is the principle that we can discover a priori necessity from a posteriori contingency".

Since then we have been discussing my expression "Kant's synthetic a priori is the principle that....."

You have been making the case that "synthetic a priori isn’t a principle", whilst I have been making the case that ""Kant's synthetic a priori is the principle that....."

This needs to be resolved before continuing with the remainder of my statement that "we can discover a priori necessity from a posteriori contingency".

Yes, "synthetic a priori" is the name of a principle, not a description….. — RussellA

I’m sticking with the text, in which, first, the content of cognitions are examined in relation to each other, and second, the domain in which certain conceptions used to form such cognitions, is examined.

It does not follow from the fact all sciences of reason contain synthetic a priori judgements as principles, that instances of particular relations of particular conceptions, are all principles in themselves.

“….The term principle is ambiguous, and commonly signifies merely a cognition that may be employed as a principle, although it is not in itself, and as regards its proper origin, not entitled to the distinction. (…) Cognition from principles, then, is that cognition in which I cognize the particular….(((2 + 2 = 4)))…. in the general…(((any quantity adjoined to any other quantity is an aggregate quantity)))….by means of conceptions. Thus every syllogism is a form of the deduction of a cognition from a principle. For the major always gives a conception, through which everything that is subsumed under the condition thereof is cognized according to a principle. Now as every general cognition may serve as the major in a syllogism, and the understanding presents us with such general à priori propositions, they may be termed principles, in respect of their possible use…..”
(A300/B357)—- (((….))) are mine —-

The relation of numbers and the arithmetic operation attached to them is an synthetic a priori judgement, subsumed under the general condition that any quantity adjoined to any other quantity is an aggregate quantity, and the arithmetic operation is cognized according to that principle, but is not itself a principle.

If you wish to stipulate that Kant’s synthetic a priori is the principle that….that’s fine, but I doubt it’s what Kant intended for it.

It does not follow from the fact all sciences of reason contain synthetic a priori judgements as principles, that instances of particular relations of particular conceptions, are all principles in themselves................................If you wish to stipulate that Kant’s synthetic a priori is the principle that….that’s fine, but I doubt it’s what Kant intended for it. — Mww

Kant writes that the term "principle" is ambiguous.

B356 The term "a principle" is ambiguous, and commonly signifies only a cognition that can be used as a principle even if in itself and as to its own origin it is not a principle.

Kant writes that on the one hand there are "principles absolutely" as used in the a priori concepts of the Categories, and on the other hand there are "principles comparatively" as used in the theoretical sciences.

B358 Thus the understanding cannot yield synthetic cognitions from concepts at all, and it is properly these that I call principles absolutely; nevertheless, all universal propositions in general can be called principles comparatively.

Paul Guyer and Allen Wood in the Introduction to the CPR talk about "synthetic a priori principles", presumably as "principles comparatively".

page 13 - At this point in the Critique Kant has completed the largest part of his constructive project, showing how synthetic a priori principles of theoretical cognition are the necessary conditions of the application of the categories to sensible data structured by the pure forms of intuition.

page 85 - Synthetic a priori judgments are contained as principles' in all theoretical sciences of reason.

I agree that the Categories are "principles absolutely"

I could change the wording of my belief to "Kant's synthetic a priori is the universal principle that we can discover a priori necessity from a posteriori contingency".

I could change the wording of my belief…. — RussellA

Good luck with that.