This is great stuff.
How do you know if something is true? What is your preferred definition of "truth"?
I don't have a preferred definition of truth. "Truth" is subjective. Definitions can create a common ground for what you call "intersubjectivity" but are unnecessary for the "intrasubjective." How do I know if something is true? If my experience is my primary standard, then I need only posit its truth (a priori or a posteriori.) For intersubjective experience, the "truth" must be posited and accepted by everyone which is in itself illogical.
There must be an original (logically necessary) truth in order to begin your infinite series of (IFF)/(THEN) statements.
Hold on to this statement.
How do you come to this conclusion? Logic is a system of AXIOMS that are tools for discovering REAL-TRUE-FACTS.
This is how I've come to that conclusion:
There must be an original (logically necessary) truth in order to begin your infinite series of (IFF)/(THEN) statements.
What is an axiom? It's an accepted self-evident truth. It precedes logic. Logic doesn't create the axiom. Logic as you stated uses it to discover "real-true-facts." But logic isn't the axiom or even the system of axioms. It's a system of reasoning which depends on axioms.
And, in reference to your excellent example, just like Schrodinger's wonderful-wonderful cat, the "photographs" are in a "quantum-super-state" up to and until the box is opened.
And is this quantum superstate empirically verifiable?
And this is a very important point, so I'm glad we're both on the same-page here.
It is only true at the point of verification.
And at that point, we can "retroactively" call it "true" colloquially, but it could never have been "true" BEFORE verification occurred.
For example, if someone hypothesized that the Sun emits invisible rays of light, before there was any scientific evidence to support their claim, they would not be "correct" and their OPINION (prediction) would not and could not be considered TRUE.
Up to and until the moment of verification, that person is not a "prophet" or a "liar". That person is indistinguishable from a lunatic (space-alien abductee).
We should NEVER "take someones word-for-it".
Only NOW can we say it is TRUE that the Sun emits invisible rays of light, and has, as far as we reasonably can tell, (retroactively) ALWAYS emitted invisible rays of light.
But it was always true. The only difference is that the information was disseminated through a standard you accept. But both the opinion and the verification could reach the same conclusion. You rely on verification because its reproducible while the opinion, not so much.
Plato's Parable of the MMORPG,
Once upon a time there were a number of people who lived in complete darkness and the only thing they could see was their computer screens.
What they saw on their screens was their reality.
The only other people they knew were people in-game with magnificent costumes and weapons.
Sure they had to fumble in the darkness in order to microwave a quick meal, or find their bed when they were exhausted, but those were merely incidental inconveniences.
Only the game was real. Only the game was shared experience. Only in-game places and people and items were quantifiable, able to be observed and verified and shared with other players (quanta).
Sometimes an individual would try to explain what kind of food they ate or describe their room (private/personal/unshared knowledge, gnosis) but since none of this information was directly relevant in-game and was fundamentally unverifiable, it was dismissed out-of-hand as unintelligible nonsense. In fact, even the language they had developed had evolved exclusively for in-game interactions, so there really weren't any proper words for "food" or "room" that were not specifically in-game references, and even more than that, since there was no taste, touch, or smell in-game, there were also no words to properly describe those sensations as well.
This argument essentially reduces to "the intrasubjective is not intersubjective; and the intersubjective is not intrasubjective." Are you suggesting that the significance in creating a distinction between the two are your personal qualifications (e.g. "unintelligible nonsense")?
It doesn't take an enormous amount of experimentation to discover that some experiences are more reliable than others.
How have you determined this?
The more reliable experiences are not 100% reliable (Hume), but they don't need to be.
What is "more"? If you don't know what 100% truth is, then how can you claim that something is not 100%?
They only need to be reliable enough to be useful.
Efficacy.
Useful and efficacious toward what?