After reviewing some anecdotal examples, I'm proposing a possible answer, called On vs. Off: The Zombie vs. Leech Theory of Grammatical Usage1 . "On" seems to have a connotation of active and pursuing while "off" seems to have a connotation of passive or required. (The other usage is the literal, location-oriented definition.)
PART 1: Zombie Vs. Leech Theory
The following is the most vivid example of Zombie Vs. Leech:
- "He feeds off his parents." (He's a leech.)
- "He feeds on his parents." (He's a zombie.)
What's the difference between a zombie and a leech? Here are a few anecdotal examples:
- "He lives on/off campus." (Location oriented.)
- "He lives on the campus." (Location oriented.)
- "He lives off the campus." (Ambiguous. Similar to "lives off the land". Could be location oriented.)
- "He lives on his parents." (Absurd. Literal parsing is like "stands on his bike." Since that's not plausible, most people would likely reinterpret this as "lives off". Thus this would be leech because zombie doesn't make sense.)
- "He feeds on excitement." (He seeks excitement. perhaps he creates it. Similar to the zombie interpretation.)
- "He feeds off excitement." (He's more passive. he likes excitement given to him. he may instigate people to argue either with himself or each other. it thrills him passively. More like the leech interpretation.)
- "He lives on rice and beans."(It might be volitional. maybe that's his diet. Zombie)
- "He lives off rice and beans."(It's the way he survives. Leech.)
Part 2: Knowledge Influences Semantic Interpretation
I need to get closer to the "ground of meaning" of the words "off" and "on". Here are some more simple and (relatively) objective scenarios.
- The cup is on the table. (This contains an assumption. The cup must have been actively put on the table. It wasn't on the table before.)
- The cup is off the table. (While this suggests that the cup [was on | might have been on] the table, it is passive in one sense: the cup never had to be on the table for it to be off the table.
- She put the cup on the table. (Active Placing. Movement Towards. "To there" Bringing Together.)
- She took the cup off the table. (Active Retrieving. Movement Away. **"From there". Bringing Apart.**)
- He lives on the apple tree. (Ambiguous. He could have a tree house or uses the apple tree for food.)
- The monkey lives on the apple tree. (Semi-ambiguous. One might prefer the "house" concept since we quickly think of monkeys living in trees. There's cognitive dissonance on the word 'on', but that could be "excused" in favor of a stronger semantic result.)
- The giraffe lives on the apple tree. (Non-ambiguous. We know giraffes do not live in trees. The giraffe eats apples or leaves.)
- He feeds on the apple tree. (He goes to there and eats, perhaps without even removing the apples! Biting the tree might even kill it. Zombie-like behavior.)
- He feeds off the apple tree. ("Off" is "retrieving". Bringing Apart. More likely that the apples are "taken off" the tree. Tree is likely to live. Leech-like behavior.)
- He lives off the land. (Under most contexts, the location aspect doesn't make sense. Location-wise, everyone "lives off the moon" so why even mention it? He retrieves life sustenance from the land.)
- He lives on the land. (Semi-Ambiguous. One might imagine a man standing on some land. Then maybe building a house or tent. But if he's "living on the table" he must be spending quite some time there so obviously he needs to get his food there too. Also, it's odd to state the obvious (most everyone "lives on land"), and it's idiomatically similar to the prior sentence. So it can be substituted for the prior. It can also have a broader meaning: not only retrieving sustenance, but also spending much time there.)
1 Disclaimer: This post is a very informal exploration of an idea. This is "original content" in the wikipedia sense: It's not based on anything other than my own thoughts, and surely suffers any and all bias that comes with that.
