“Yet no nanocomputer or other complex circuit was built for a decade and a half. [32]  We had the devices. What we do not have, still, is simply the infrastructure that macroscopic technology takes for granted: the ability to sort and test parts; to cut and join materials; to create frameworks that can hold devices in designed relationships, and the ability to place parts into such frameworks.”

J Storrs Hall. “Where Is My Flying Car?: A Memoir of Future Past.”

“The principles of modality are, however, not objectively synthetical, for the predicates of possibility, reality, and necessity do not in the least augment the conception of that of which they are affirmed, inasmuch as they contribute nothing to the representation of the object. But as they are, nevertheless, always synthetical, they are so merely subjectively. That is to say, they have a reflective power, and apply to the conception of a thing, of which, in other respects, they affirm nothing, the faculty of cognition in which the conception originates and has its seat. So that if the conception merely agree with the formal conditions of experience, its object is called possible; if it is in connection with perception, and determined thereby, the object is real; if it is determined according to conceptions by means of the connection of perceptions, the object is called necessary.

The principles of modality therefore predicate of a conception nothing more than the procedure of the faculty of cognition which generated it. ” (emphasis mine).

--- Immanuel Kant, “The Critique of Pure Reason.”

== possible - impossible
== existing - non-existing
== necessary - contingent

The principles of modality need to be stated explicitly when making predictions, i.e. we have to specify methods and related potential failure of imagination, esp. wrt possibility.