The formation rules for meaningful metaphorical discourse do not have unrestricted compositionality. While "The fruit borne by Quantum Mechanics is sometimes bitter" is probably meaningful, "The fruit borne by Quantum Mechanics is sometimes elongated" has no meaning unless we choose to assign one to it. The latter sentence takes the metaphor too far.
A sign of metaphor being pushed too far is that classical logic has the appearance of failing. It appears to be neither true that the fruit of Quantum Mechanics is sometimes elongated nor that the fruit of Quantum Mechanics is never elongated, contrary to bivalence. To ask which is the case is to be silly. The same apparent failure of classical logic can occur when we make too involved inferences from a metaphorical claim, for instance when we conclude that Quantum Mechanics is partly made of carbon atoms, because only plants bear fruit and all plants are partly made of carbon atoms.
Here is a different kind of metaphor (I heard this metaphor—though I don't remember if it was identified as a metaphor—in discussion at INPC): The average plumber has 2.3 children. Let's press on. Stipulate, no doubt contrary to fact, that exactly half of all plumbers are male and exactly half of all plumbers are female. So, is the average plumber male? No. Is the average plumber female? No. Is the average plumber human? Certainly (supposing there are no alien plumbers). So, the average plumber is a human who is neither male nor female. Now, maybe there are such rare humans (this is a difficult question about the metaphysics of sex), but since by stipulation none of them are plumbers, surely the average plumber isn't one of them. Wondering about this bit of weirdness is, however, silly. It is taking the metaphor of the average plumber too far. Once we start saying that the average plumber is a human who is neither male nor female, we take our metaphor beyond the narrow region of the space of sentences where it makes sense.
Now, some metaphysicians, including me, think that in an important sense there are no tables or chairs. There are only particles or fields arranged tablewise or chairwise. It is a tough problem for these metaphysicians to defend their own use of ordinary language about tables and chairs—their saying things like "There are ten chairs in the room."
I think our ordinary language about artifacts has some things in common with metaphorical language. Take something like the question of how much of the wood of the table you can replace, and in how large chunks, while maintaining the same table? I think one can have a sense of discomfort with the question. After enough fast replacement of wood, one is tempted both to deny that one has the same table and to deny that one has a distinct table. The question seems to be a matter for our decision—much as it is a question for our decision whether we count last year's average plumber, with his/her/its 2.29 children, as the same individual as this year's average plumber with his/her/its 2.30. In the plumber case, the decision is a decision what to understand identity across time in the metaphor as standing for (maybe by saying that the average plumber is the same last year as this year we want to metaphorically signal that there was no en masse replacement of plumbers). And, I think, the ordinary folk think there is something a bit humorous and unserious about pressing the question whether after the replacement we have the same table, just as they would in the plumber case.
These things suggest that when we ask whether we have the same table, we can be pushing language too far, just as we sometimes do in metaphorical cases. And this, in turn, suggests that we should not take "There is a table here" at face value.
I will stop short of saying that our ordinary language of tables and chairs is literally metaphorical, that "their existence is metaphorical". Instead I'd like to say that our ordinary language of tables and chairs behaves in certain important respects metaphorically. Among these respects is that we should not expect arbitrary compositions of such language to be meaningful, and we should not expect to have classical logic hold on the surface level.
I actually think classical logic holds even in cases of metaphor. But it holds not at the linguistic level, but at the level of the propositions expressed by the metaphorical claims. "The average plumber has 2.3 children" expresses the same proposition as some sentence like "The average of the numbers of children had by plumbers is 2.3", and the latter sentence better reflects the logical structure of the proposition.