An ELT Glossary : The mandative subjunctive

The so-called "mandative subjunctive" is the use of the base form of the verb in a "that" clause after verbs and other expressions expressing concepts such as advice, recommendations, suggestions, orders, requests etc. etc. In all but the third person singular, it is impossible to distinguish it form the present simple unless the verb be is involved, but with these subjects it means that there are to possible constructions:

a) with the present simple

I insist that he pays for the damage in full.
We recommend that the inquiry is finished before June
I suggest that he thinks more carefully about it
It is important that they are fully informed about this.

b) with the mandative subjunctive

I insist that he pay for the damage in full.
We recommend that the inquiry be finished before June.
I suggest that he think more carefully about it.
It is important that they be  fully informed about this.

Notice that this gives a more formal style to the text.

Another way of looking at this use of the base form is simply to see it as an infinitive following an ellipted should. All of these sentences could also be expressed as:

I insist that he should pay for the damage in full.
We recommend that the inquiry should be finished before June.
I suggest that he should think more carefully about it.
It is important that they should be  fully informed about this.

Notice that the same possibilities are often possible in sentences with an if clause :

If that is true...  =  If that be true...  =    If that should be true...
If he denies it... =  If he deny it... =  If he should deny it...