Can who replace whom?

Today’s English
April 15th, 2017

Some people who strictly follow formal English grammar even in speech are shocked to see the use of “who” in the place of “whom”.  Let’s see the differences:

1.Who versus whom
Who is the subject of a sentence whereas whom is the object.
Who sent you such a mail? (Who as a Subject)
Whom did you call for help? (Whom as an object)

2.Modern English prefers “Who” to “whom” especially in spoken English
It’s widely accepted in today’s English by modern grammarians and authentic dictionaries such as Cambridge and Oxford that “who” can be used instead of “whom”

Whom did you meet yesterday?  (Very formal and not normal in modern English)

Who did you meet yesterday? (Informal and very common in modern English)

To whom did you give the book? (Rarely used by modern English speakers)
Who did you give the book to? (Modern usage)

For whom are you waiting? (Rarely used nowadays)
Who are you waiting for? (Modern English)

3.Who or whom can be used or omitted only in defining relative clause, never in non-defining relative clause:

The teacher (who) I met yesterday is doing Ph.d. (whom is avoided in spoken English)

Mr.Karthick,whom/who everyone knows here very well is actually my relative. (Here who or whom cannot be omitted).

“The old order changeth yielding place to new And God fulfills himself in many ways Lest one good custom should corrupt the world.” -Alfred Tennyson, “Idylls of the King"