Notes from the contributor of the question: I now believe that this post is not useful at all. Please see this other post on the same topic.
This question asks when a past tense indicative mental-state verb (English examples: to know, believe, feel) may introduce a présent conditionnel mental-content clause (example: something would or would not be the case).
The purpose of this post is to bring out that theory more fully.
In what follows, I will briefly recap what we learned in the older posts (so people don't have to read them) and ask a series of related questions for the purpose stated.
The example of a past tense indicative mental-state properly introducing a présent conditionnel mental-content was from Camus's The Stranger, as highlighted below:
En me réveillant, j’ai compris pourquoi mon patron avait l’air mécontent quand je lui ai demandé mes deux jours de congé : c’est aujourd’hui samedi. Je l’avais pour ainsi dire oublié, mais en me levant, cette idée m’est venue. Mon patron, tout naturellement, a pensé que j’aurais ainsi quatre jours de vacances avec mon dimanche et cela ne pouvait pas lui faire plaisir. Mais d’une part, ce n’est pas de ma faute si on a enterré maman hier au lieu d’aujourd’hui et d’autre part, j’aurais eu mon samedi et mon dimanche de toute façon. Bien entendu, cela ne m’empêche pas de comprendre tout de même mon patron.
Marking it for tense, we get:
(B0') Mon patron, tout naturellement, a pensé[a past tense] que j’aurais[présent conditionnel] ainsi quatre jours de vacances avec mon dimanche
The sentence in which a past tense indicative improperly attempts to introduce a présent conditionnel mental-content clause was derived from this other passage from The Stranger:
J’étais fatigué. Le concierge m’a conduit chez lui et j’ai pu faire un peu de toilette. J’ai encore pris du café au lait qui était très bon. Quand je suis sorti, le jour était complètement levé. Au-dessus des collines qui séparent Marengo de la mer, le ciel était plein de rougeurs. Et le vent qui passait au-dessus d’elles apportait ici une odeur de sel. C’était une belle journée qui se préparait. Il y avait longtemps que j’étais allé à la campagne et je sentais quel plaisir j’aurais pris à me promener s’il n’y avait pas eu maman.
You may need to be told that, here, Meursault (first person narrator) has just sat through a vigil for his poor maman and upon rising and coming out of the mortuary expressed what he sensed, or felt, as above.
The sentence said to be ungrammatical because of an improper attempt to introduce a présent conditionnel mental-content with a past tense mental-state verb was generated this way. I asked whether, factually assuming that Meursault was regretting the walk he could not take at the very moment he "sentais" (as opposed to a walk that had not taken place at an earlier part of the morning), we could express that situation with the following:
(A0') Je sentais[a past tense] quel plaisir je prendrais[présent conditionnel] à me promener s'il n'y avait pas maman.
I was told that (A0') was ungrammatical. See comments to Kyrio's answer in this older post.
Now for the explanation of why the one sentence is grammatical while the other is ungrammatical, see radouxju's answer in this older post.
If I am reading that answer correctly, it may point to two differences between (A0') and (B0').
Time: In (A0') mental-content is coeval with mental-state, but in (B0') mental-content is at a future relative to mental-state (i.e. Meursault regets not being able to take a walk right then and there, but the vacation would happen at a future relative to the boss's thinking about it).
Reality: In (A0') mental-content is irreal, but in (B0') it is possible (i.e. the walk is ruled out and irreal because of maman's funeral, but the vacation remains possible and in fact becomes actual in the novel).
The question is which of the two, time or reality, is the critical factor. I will try to bring this out in a series of questions that can be answered yes or no. If time or reality is dispositive, I believe, we would get clear unhesitating yes or no to them. If they are unclear and other factors are at play, I would want to learn what those other factors are.
If time is critical, that may be expressed this way: A past tense indicative mental-state verb may properly introduce a présent conditionnel mental-content clause if the content will be at a future relative to the state but not if they are coeval.
To test that theory, we ask the following.
(T1) Imagine a slightly different novel which tells us exactly when Meursault did what he did. For example, we are told that at 10 a.m. he, realizing that it was time for his regular morning walk, "sentais" what a fine walk he would have commencing at 10 a.m. and ending at 10:30 a.m. The walk remains ruled out (irreal) as in the actual novel. In this example, mental-content is imagined as commencing coevally with mental-state and extending into a relative future. Sentence (A0') expressing this situation is now grammatical. Yes or no?
(T2) Just like (T1), except that Meursault "sentais" at 9:55 a.m. Here, the irreal mental-content lies entirely at a future relative to mental-state. Sentence (A0') expressing this situation is now grammatical. Yes or no?
(T3) The boss, instead of thinking of Meursault's enjoying his vacation at some future date, thinks in terms of Meursault's having a permission for vacation both then and there (coeval to "a pensé") and into the immediate future. The vacation remains possible (and becomes actual) as in the actual novel. In other words, (B0') in the novel is replaced by the following:
(C0') Mon patron, tout naturellement, a pensé que j’aurais ainsi la permission pour quatre jours de vacances avec mon dimanche
This sentence for the situation imagined is now ungrammatical (because of the coeval bit). Yes or no?
(T4) Just like (T3), but the boss thinks of Meursault's receiving the vacation (or the permission for it if you prefer), which would be instantaneous and entirely coeval with "a pensé." (If you like, you can imagine the boss continuing to think so as he grants the permission.) In other words, the sentence is replaced by:
(D0') Mon patron, tout naturellement, a pensé que je recevrais ainsi (la permission pour) quatre jours de vacances avec mon dimanche
This sentence for the situation imagined is now ungrammatical. Yes or no?
If we believed "time is critical" I think we'd say yes to some of the above.
Suppose we believed reality was critical instead. I.e. a past tense indicative mental-state verb may properly introduce a présent conditionnel mental-content clause if the content remains possible but not if it is ruled out and irreal.
(R) Imagine a different novel, in which Meursault, upon "sensing" as he does, goes on his morning walk (the funeral be damned). Thus, we've changed only the reality from irreal to possible, leaving everything else as before. For this situation, (A0') is now grammatical. Yes or no?
Again, if we believed "reality is critical," we would say yes to (R).
I think it would be weird if introduction (of mental-clause by mental-state) is proper only when time = future and reality = possible and improper only when time = coeval and reality = irreal, because the theory would then be unable to tell us about what is grammatical in the other two permutations. Be that as it may, we can imagine the following changes to the novel as well.
(M1) Meursault "senses" at 10:00 a.m. about a 10:00 to 10:30 a.m. walk (i.e. coeval and future) and the walk is now a possibility and in fact becomes actual. For this situation, (A0') is now grammatical. Yes or no?
(M2) Just like (M1), but the "sensing" takes place at 9:55 a.m. (i.e. only future). For this, (A0') is now grammatical. Yes or no?
(M3) The boss refuses the vacation, making it irreal, and he thinks in terms of "recevoir," making it coeval. For this, (D0') is now ungrammatical. Yes or no?
Please note that I am not trying to reduce French to one or two bright-line rules. I want to learn the extent to which the proposed factors are explanatory, anticipating that it may be partial. If we need other factors to understand the issue completely, I want to learn what they are.
At the same time, I believe the questions should all be capable of a yes or no answer. After all, a sentence is either grammatical or not for a given situation. Therefore, I would appreciate an answer that gives yes or no, wherever possible, before adding anything else.
P.S. I consider this question to be fully answered by the first comment to it (by GAM PUB).