French Conjunction 'Tant Que" Doesn't Need Subjunctive

Tant que is a conjunctive phrase (locution conjonctive) that, unlike many other conjunctive phrases, does not need the subjunctive. It means "as / so much as" or "as long as / while / since," depending on the context.

Tant que is a phrase that communicates certainty and intensifies quantity, frequency, degree and the like. Thus, there is really no reason for the subjective subjunctive.

Tant que tu es ici, tu peux m'aider. > As long as / Since you're here, you can help me.
J'ai tant lu que j'ai mal aux yeux. > I read so much that my eyes hurt.
Il a tant manger, qu'il est malade. > He ate so much that he's sick.
Tant que tu es la, cherche mes lunettes. > As long as / since you're here, look for my glasses.
Tu peux rester tant que tu veux. > You can stay as long as you want.

'Tant Que' vs. 'Autant Que'

Do not confuse tant que with autant que, another conjunctive phrase that seems similar but is really more about equalizing and comparisons. It, too, is an adaptable and widely used phrase in French that has a number of possible meanings in English: as far as, as / so much as or as long as / while. So while tant que is about intensity, autant que is about balance. Autant que communicates conjecture and doubt, so the verb following it should be in the subjunctive, indicated in bold below:

Autant que je me souvienne... > As far as I remember...
Autant que je vous le dise tout de suite. > I may as well tell you right now.

Other French Conjunctive Phrases

A conjunctive phrase is a group of two or more words that function as a conjunction that links clauses. French conjunctive phrases end in que, and many, but not all, are subordinating conjunctions, rather than coordinating conjunctions, that require a subjunctive verb. One asterisk below indicates those that take the subjunctive.

à condition que* > provided that
afin que* > so that
ainsi que > just as, so as
alors que > while, whereas
autant que* > as far as / as much as / while
à mesure que > as (progressively)
à moins que** > unless
après que > after, when

à supposer que* > assuming that
au cas où > in case
aussitôt que > as soon as
avant que** > before
bien que* > although
dans l'hypothèse où > in the event that
de crainte que** > for fear that
de façon que* > in such a way that
de manière que* > so that
de même que > just as
de peur que** >for fear that
depuis que > since
de sorte que* > so that, in such a way that
dès que > as soon as
en admettant que* > assuming that
en attendant que* > while, until
encore que* > even though
jusqu'à ce que* > until
parce que > because
pendant que > while
pour que* > so that
pourvu que* > provided that
quand bien même > even though/if
quoi que* > whatever, no matter what
sans que** > without
sitôt que > as soon as
supposé que* > supposing
tandis que > while, whereas
tant que > as long as
vu que > seeing as/that

*These conjunctions must be followed by the subjunctive.
**These conjunctions require the subjunctive as well as the ne explétif, a more formal negation that uses ne without pas.