How to parse. ...

132 IRREGULARITIES. [Par. 200.
In this last example two principles are at work.
The regular construction would have been
(1) "It that says so is you."
Here steps in (III.) the desire to avoid the harshness of "it," used so emphatically; hence "it" is
deprived of its emphasis by being separated from
its Relative " that."
(2) " It is you that says so."
Here steps in (II.) "confusion" between this construction and the straightforward construction "You
say so "-resulting in the idiom logically incorrect,
but by process of custom stamped as perfectly good
English: -
(3) "It is you that say so."1
200 Irregularities are very common (i) with the
Relative Pronouns and Relative Adverbs, (ii) with
Adjectives and Adverbs of Number and Amount.
A few of these irregularities are given below, in
order to prepare the reader for dealing systematically with all irregularities in the English shape.
In every case the same method will be adopted,
viz. to askI. IVhat would be the regular construction?
II. What is the cause of irregularity?
I See also Par. 160.