Who = Who

·       WHO = HE (A NEAT TRICK)

Substitute 'who' with the word 'he'. If that part of the sentence still makes sense, then 'who' is almost certainly correct. (These are from the examples to the left.)

He paid for the meal. (< sounds ok)
("Who paid for the meal?" is correct.)

...he lives in the hut... (< sounds ok - "who" is correct)

...he is in charge. (< sounds ok - "who" is correct)

...to he? (< does not sound ok - "who" is wrong)

'Who' and 'he' are always the subjects of verbs. They are said to be in the subjective case. This is why the trick works.

WHO = THEY

In order to perform this trick for plurals, you will have to substitute 'who' with the word 'they'.

I met the people who were on the plane.
...they were on the plane. (< sounds ok - "who" is correct)