I have read that in English, reason adverbial clauses introduced by because can be focalized using the it is... that... cleft construction, whereas those introduced by since resist such focalization (The Cambridge Grammar of the English Language, 2002, p. 732). This observation leads me to the following question: When someone offers a causal explanation for an event using a because-clause, and I wish to rebut their assertion about the cause—that is, to sever the link between the because-clause and the main clause—what I am doing semantically amounts to saying that the proposition in the because-clause is not the cause. This constitutes a negation of the causal relation itself, rather than a negation of the content within the causal clause while preserving the causal relation. To put it concretely, it is not transforming:
I am very angry because he ate my cake.
into:
I am very angry because he didn’t eat my cake.
Rather, it means excluding “he ate my cake” from the set of all possible causes for “I am very angry.” Returning now to the contrast between because and since: if the speaker’s reason clause is introduced by since, and I want to rebut them by denying the connection between the main clause and the proposed cause, then—given that since-clauses cannot be focalized via the it is... that... structure—I apparently cannot construct a corresponding negative cleft (it isn’t... that...). In such cases, what negation operator should I use instead?
More broadly, I don’t want to confine this inquiry to this single example. What interests me is whether there exists a systematic negation operator—one that applies not just to one or two specific subordinators but to an entire class of adverbial clauses defined by certain properties (much like the it’s...that... cleft applies systematically)—capable of severing the semantic link between an adverbial clause (note: a full clause, not merely a phrase) and its matrix clause. If such an operator exists, what is it? And does it, like the it’s...that... cleft, come with restrictions? If so, what properties must a subordinator have in order to fall under (or be excluded from) the scope of such an operator? (Please note that my question here concerns adverbial clauses across multiple semantic types—at the very least, those I have listed below—and is not limited solely to causal adverbial clauses.)
P.S.
Naturally, the answer may depend on the semantic type of the adverbial clause. It may be that only certain types—conditional, causal, purposive, concessive, manner, or temporal adverbial clauses—are amenable to such a negation operator; and further, that even within those types, only certain subordinators allow it. I would like to know, for each of these adverbial clause types, what the corresponding systematic negation operators are (if indeed they can be targeted by such operators at all).
To make the systematic negation operator I’m after clearer, I’ve laid out a somewhat elaborate preamble.