Meaning of 'up/down' after a verb [closed]

The best way to think about these is as part of the verb itself. Drink up, meaning "finish your drink" has an acceptedly different meaning to drink.

Up is, of course, a preposition and an adverb implying a spatial difference in height from a low point to a high point. Hence, lift up more closely specifies the action of lift. But in the instances you have described up has lost its original adverbial force.

There are two ways we could classify this up. We could either analyse every occurrence of it and try to draw it a secondary meaning of the word up where it has become a sort of intensifying adverb, presumably with the idea of up to the end, but this in part relies upon etymology, and such a pursuit is not part of your question. I suspect that many of your examples had different etymologies too, and that some were formed by analogy to others.

The alternative method, which I would personally choose – since it's a little more conservative and avoids Byzantine classification – is to say that although they're comprised of two words really they're one semantic and syntactic unit.

This is something of a problem in linguistics which I'm beginning to study more closely now, which boils down to: can you talk about a word or words in isolation, or must you discuss them as part of the sentence, paragraph and discourse in which they occur? Is it valid to chop up a sentence down to the word? Remember, we have certain set phrases in English, such as "to ride a bike" where the riding, you will agree, is very different to the riding of "to ride a horse". While a dictionary might index two meanings or more of "ride", you might consider them to be separate phrases. There are better examples and I welcome comments giving them.

This will apply to down as much as to up, I hope.

All right, I'll answer this because @Cerberus appears determined to shame me into it.

The problem is, up and down when used in phrasal verbs have wildly different meanings, and it is difficult to find common ground among them.

Verb + up is often used as an intensifier or signifier of completion. For example, if you screw up you make a significant blunder. And if you eat something up, you devour it completely. Similarly, down is often used to mark completion: nail it down, get it down (as learning a skill), shoot it down (in the metaphorical sense), and so on.

Still, there are too many other cases. Lock up may or may not qualify. And you can be locked up and locked down at the same time. But the up and down don't have to mean the opposite thing, and often don't. To take something up is different from to take something down. The opposite of take something down is to put something up.

You can screw something up, sweeten it up, mark it up, look it up — all different in meaning. You can knock someone up and knock someone down—two unrelated processes—but while you can soften someone up you can't turn around and soften someone down.

There really aren't any handy shortcuts. You just have to learn when to use up and down in each phrasal verb you encounter.