One of the well-known (but slightly lesser-studied) varieties of ellipsis (in English) is called “null complementation.” It’s involved in understanding sentences like these:
- Do you understand? (what I’ve been saying)
- I have to refuse. (to do what you asked me to do)
- Wow, your wristwatch is really similar! (to that other watch we’ve been talking about)
Certain verbs allow this, and others don’t. Famously (is that the right word?), _try_ does but _attempt_ does not: _Just try, it won’t hurt! is okay, but *_Just attempt!_ is out. (Exception: fine print in advertisements that say: _do not attempt_). _Know_ also allows it. (Yes, yes, I know).
Okay, so here’s the story. I was on the bus the other day and there were two people who seemed to be friends nearby. The driver was turning the corner, but stopped to let people pass. Apparently he was allowing too many people to pass, and one of the friends said, “Come on, go, go!” (softly, as though to the driver but actually for the benefit of her friend; sort of a strange self-directed version of a pseudo-imperative meant for the benefit of a hearer). Then the other friend said,
> I know!
The puzzle: what did she know?