Nominal clause plus subjunctive

Question

I wonder if the indicative present is good in the clause:

it is the requirement that, when John arrives, Mark be here

The answers are detailed but I wish to discuss the case "when becoming if" in order that I understand better: When we wish say "if John arrives at the same time" I believe nothing changes.

it is the requirement that, if John arrives, Mark be here

When we wish to say "if John arrived yesterday", then I do not see why it is not the past subjunctive. Past because it is on yesterday that we are focusing, subjunctive because it could happen or not (because of the if). So,

it is the requirement that, if John (had?) arrived, Mark be here

Is it with had or without ? what would be the difference ?

I changed the title.

Answer 1

NOTE: Since you have rewritten your question to examine a conditional construction with if instead of a time adverbial with when, I have banished my original answer to the end.

If I understand your new question correctly, you are asking what verb forms or constructions should be used with condition clauses (IF clauses) expressing either past or current eventualities when the consequence clause is a ‘mandative subjunctive’.

That is, you have a situation where an authority (let’s call him The Boss) gives an order to a subordinate (Mark) to be present under various circumstances involving John’s arrival.

• The first thing we have to note is that a mandate, whether indicative or subjunctive, can only refer to an event which lies in the speaker’s future. The Boss may require Mark to be present in the future, but not in the past:

  ^okBOSS: Be here this afternoon! ... which might subsequently be reported as
  ^okIt was required that Mark be present that afternoon.
  But these are absurd:
  ^∗ BOSS: Be here yesterday!
  ^∗ It was required that Mark be present the previous day.

  This is why a when clause with a mandative must employ a tense which expresses simultaneity with the mandated event. This sentence is absurd:

  The Boss requires^present that Mark be present when John arrived^past yesterday.

  This restricts the ability of mandative be to influence the other tenses in the sentence. The clause in which it falls is always actualized after the action of its head clause, regardless of what tense is employed in the head clause.

• The second thing we have to note is that in Present-Day English, a condition (IF) clause which qualifies an imperative or mandate must be cast in the realis mode. It is true that in older English a condition clause in these situations often employed a ‘subjunctive’ form:

  If music be the food of love, play on. —Shakespeare, Twelfth Night
  If this be treason, make the most of it! —attributed to Patrick Henry

  In those days, be was a true subjunctive, expressing subordination. But today, using such forms expresses irrealis mode: a tentative or counterfactual supposition—except in mandatives. A ‘mandative subjunctive’ is in all circumstances a realis expression; and we are not permitted to join an irrealis condition to a realis consequence.

  Thus, The Boss may say this, with a realis condition:

  ^okA1. I require^realis that if John arrives^realis you be^realis here. which might subsequently be reported as
  ^okA2. It was required^realis that if John arrived^realisMark be^realis there.

  And he may say this, with an irrealis condition:

  ^okA3. If John arrived^irrealis I would^irrealis require that you be^realis here. which might subsequently be reported as
  ^okA4. If John had^irrealis arrived it would have been^irrealis required that Mark be^realis there.

  But he may not say this:

  ^∗ B1. I require^realis that if John arrived^irrealis you be^realis here. so this is impossible, too:
  ^∗ B2. It was^realis required that if John had^irrealis arrived Mark be^realis there.

  Note the difference: In A3 and A4, the irrealis condition qualifies the action of mandating, which can be and is cast in the irrealis mode. But in B1 and B2, the irrealis condition qualifies the action mandated, which cannot be cast in the irrealis mode. Consequently, B1 and B2 are ungrammatical.

  As you point in the comments, however, B1 and B2 are grammatical if their middle verbs do not bear an irrealis meaning—that is, if the mandate is based not on a counterfactual but on a still-undetermined prior arrival:

  ^okB3. There are rumors that John arrived yesterday. I require^realis that if John in fact arrived^realis yesterday you be^realis here tomorrow. which might subsequently be reported as
  ^okB4. It was^realis required that if John had^realis in fact arrived Mark be^realis there.

---

ANSWER TO THE ORIGINAL QUESTION:

It is the requirement that, when John arrives, Mark be here.

1. The when clause is not a relative clause but an ordinary adverbial time clause modifying the subordinate clause Mark BE here; and the that clause is not a relative clause but an ordinary nominal clause acting as the complement of requirement. So the matter of restrictiveness does not arise.

2. The when clause not only may, it should be expressed employing the indicative form. Adverbial clauses are governed by their head clauses only for tense, not for mood.

   ^okIt will be a good thing if Mark is here when John arrives.
   ^okIt would be a good thing if Mark were here when John arrives.
   ^∗ It would be a good thing if were here when John arrive.

   Note that although the tense in the adverbial clause is determined by the tense of its head clause, it is not necessarily expressed with the same form or construction as the head clause.

   It was a good thing that Mark was here when John arrived.
   It would have been a good thing if Mark had been here when John arrived.

3. The ‘present subjunctive’ form with commands and desires is usual in US speech and writing, and it is becoming more common than it used to be in Br speech and writing; but it is not obligatory in either: it may also be expressed with an ordinary indicative, or with should. But in all these cases the adverbial will take the same form.

   It is the requirement that, when John arrives, Mark be here.
   It is the requirement that, when John arrives, Mark is here.
   It is the requirement that, when John arrives, Mark should be here.

---

^∗ marks a usage as unacceptable

Answer 2

This kind of subjunctive is preferred in written AmE. By the way, the that-clause is not a non-restrictive relative clause, but the subject placed in end-position by means of "it" as a precursor.

You can reformulate the sentence as:

• That Mark be here is the requirement when John arrives.

For me, your formulation sounds rather unnatural. I think you can use the indicative as well. But I would choose another formulation such as:

• Mark should be here when John arrives, that is necessary.