RON 神对于比较省略的回答，有个问题望大家解惑~~

Is the ONLY rule to decide whether helping verbs are needed is through context? Or can I say if there are NO OBJECT in the sentence, then I must include helping verb, as the examples sited below shown (and same rules apply in the above two examples?)

I eat faster than you (correct)

I eat apple faster than you do (correct)

I eat apple faster than you (incorrect).

there are two instances in which a helping verb is needed:

1) change of tense (see the example above)

2) the sentence is ambiguous without the helping verb.

as far as #2, consider the following two sentences:

i can lift more weight than my brother

i know more about shakespeare than my brother

the second of these is incorrect, because it's ambiguous -- it could carry one of two meanings:

1) i know more about shakespeare than my brother knows about shakespeare

2) i know more about shakespeare than i know about my own brother

the first is not ambiguous in this way:

1) i can lift more weight than my brother can lift --> PROPERLY PARALLEL ("i" and "my brother" are parallel)

2) you can't construct a meaning that is like #2 above, since "weight" and "my brother" are not parallel constructions.（这里的结构不平行指的是逻辑含义上的不平行？还是概念上的？）

your final sentence -- "i can eat an apple faster than you" -- is actually ok, since it is like my latter example: there is no ambiguity, and there is also no change of tense.（只要时态上不改变就不用补出情态动词can 了吗？难道不会有eat you 的歧义？这和前面的brother和weight 的不平行有什么联系吗？此处也是不平行所以没有歧义？）