I know this is incorrect:
(a) Peter has more pencils than pencils of Jack
and this is correct:
(b) Peter has more pencils than Jack has
But I want to understand what is the exact reason why (a) is incorrect. Is this illogical comparison or what?
But then why is the following correct:
Peter has more cycles today than yesterday.
Clearly, the above is not interpreted as:
Peter has more cycles today than yesterday has cycles.
No. "Yesterday" does not have bicycles. That would be completely illogical and no-one would interpret it to mean that. Peter has bicycles today. Peter had bicycles yesterday. Today, Peter has more bicycles than he (Peter) had yesterday. This can be (and regularly is) shortened to "Peter has more bicycles today than yesterday". We simply know this means "Peter has more bicycles today than [he had] yesterday".
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.
But then, why is this not correct:
Peter has more pencils than pencils of Jack
A member above remarked that this sentence can be interpreted as "Peter possesses more pencils than the pencils belonging to Jack possess".
Peter has five pencils.
Jack has four pencils.
Peter has more pencils than Jack [does]. (The "does" is optional.) Short for "than Jack has pencils."
This compares the number of pencils Peter has to the number of pencils Jack has.
Peter has five pencils.
Peter has four pens.
Peter has more pencils than he has pens. Peter has more pencils than he does pens. Peter has more pencils than pens.
This compares the number of pencils Peter has to the number of pens Jack has.
Peter has more pencils than [pencils of Jack] -- there is no appropriate comparison. "Pencils of Jack" cannot have their own pencils.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.