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(A): Oh dear, nobody has cut the grass.
(B1): John was supposed to do that.
(B2): John was supposed to have done that.

Dear Ricky,

In response to (A), both (B1) and (B2) are fine. Sentence (B2) is the past perfect, and in "textbook grammar" it would probably be preferable because it is talking about something that should have been done at some indefinite point in time in the past before another point in time in the past. The past perfect talks about one of two things:

1.) a period of time that started before and continued up to (and possibly past) another past point in time; or,
2.) an indefinite point in time in the past (that is, a point in time in the past that is unknown or unstated) before another past point in time.

For example:
1.) When George W. Bush began his second term, he had been President for 4 years.
2.) Before George W. Bush became President, his father had been President.

Because John was supposed to have cut the grass before another point in time in the past (that is, some point in time before now), (B2) is probably better. However, in informal English, you can sometimes replace a perfect tense with the simple past, and it would be easy to imagine a native speaker saying (B1).
(A): Oh dear, nobody has cut the grass.
(B1): John was supposed to do that.
(B2): John was supposed to have done that.

Dear Ricky,

I think that I was wrong. According to chart 9-9 on page 166 of Azar's "Understanding and Using English Grammar, Third Edition" the following is correct:
"Jack was supposed to call me last night. I wonder why he didn't."
Therefore, (B1)--not (B2)--is correct. If (A) read, "When I got to the golf course, nobody had cut the grass," then (B2) would be the correct answer. (That would also be the correct time to use the past perfect.) Once again, my previous answer was incorrect, but I think that I have inadvertently answered your original question: "When should we use which ?"

By the way, in case I have screwed up again, I hope someone will be kind enough to fix my mistake.
Last edited by kafkaesque
As Kafkaesque says, either response is correct, and acceptable. The complement of "be supposed [to]" is an infinitive, whether simple infinitive("to cut") or perfect infinitive ("to have cut"). Nuances do sometimes exist in the choice of complement form.

If the speaker is referring to the action from the point of view of the initial plan, request, or instruction, the infinitive is sufficient. It's as if the speaker were saying "I/someone else told him to cut the grass." Google examples:

"”The boy was floating on a boogie board and was supposed to find a turtle before he came back to the party. He found the turtle, but when the turtle touched ...
http://www.rhapsodic.org/dream/archives/2003/10/index.php

"” This is the story of "Operation Market-Garden," the code name of the offensive which was supposed to bring the Allies victory before the end of 1944. ...
http://www.wwiibooks.com/new_video.html

"” My one major disappointment was the shipping problems I had. My purchase was supposed to arrive before christmas but was not received until 12/28.
http://www.epinions.com/pr-Online_Stores_ Services-eGeneralMedical/display_~reviews

"”My one friend bought a laptop from DELL and it was supposed to arrive before the semester started. It didn't arrive until three months later!!! Sherry Says: ...
rose.geog.mcgill.ca/wordpress/?p=10

On the other hand, if the total completion of the action is important, the perfect infinitive expresses that idea more accurately than the simple onfinitive. It's as if the speaker were saying "He was supposed to have the grass all cut by now."

"” So John had ordered a new Ford Model A two-door car. It was supposed to have arrived (i.e. be there) before March 1. It did not come, so John was becoming upset. ...
emmitsburg.net/archive_list/articles/ people_articles/john_fuss/john_fuss_part_4_5.htm

"” The document was supposed to have been published before the midterm elections but was delayed for fear of voter reaction. A couple of years ago, ...
http://www.fff.org/freedom/0195a.asp

"”a prop gun supposedly containing a dummy bullet was fired at his chest – the bullet was supposed to have been removed before the scene started. ...
http://www.epinions.com/ mvie-review-5D80-203FFCA4-3A4F1380-prod4

These are examples of careful attention to aspect. In fact, many speakers use the two forms interchangeably, often choosing the simple infinitive when the perfect infinitive would be more accurate.

Marilyn

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