> "is-to-see" is not a contiguous unit You can insert stuff between "is" and "to-see" (and between "to" and "see", I hope you agree) because English mostly par

> "is-to-see" is not a contiguous unit You can insert stuff between "is" and "to-see" (and between "to" and "see", I hope you agree) because English mostly parses into left-branching trees, which is the only reason why you can't insert stuff between "see" and "-ing". Natural languages don't liberally mix left-branching structures and right-branching ones because they're hard for people to understand. E.g. Pinker's "The rapidity that the motion that the wing that the hummingbird has has has is remarkable" is grammatically correct but not easily understandable. The contiguity or lack of it operates on a different conceptual plane to whether a "word" can be inflected or not. > loose analogy To take some example language from your reply, some people speak this as two words, others (e.g. some Americans) as a compound word. Because the concept of a word is not well defined, the boundary between morphology and syntax is blurred. Putting "is" and "to" noncontiguously before a verb is the same as putting "-ed" after a verb. They are both "inflections".