On one hand, possessive case is one of the simplest topics and still there are few nuisances. Should I say:

Tom, professor assistant, was entering the lab.


Tom, professor's assistant, was entering the lab.

Tom doesn't belong to professor, but words professor and assistant definitely have the possessive link - assistant OF the professor

2 Answers 2


Certainly, Tom does not belong to professor but the professor can still say, "He is my assistant", can't he?

That said, "Whose assistant? ~ Professor's". The possessive is fine there.

Out of those two,

Tom, (the) professor's assistant, was entering the lab.

is okay.

  • Why did you put the article before professor's assistant? Oct 8, 2014 at 13:00
  • Because we are talking about Tom and his specified post. Compare - Denis, the principal, entered Xavier's college and students clapped
    – Maulik V
    Oct 8, 2014 at 13:17

Tom, the professor's TA, entered the room. is how it would be said in American English. Substitute "assistant" for "TA" (teaching assistant).

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