In French, the verb mood you choose depends on how you see the action. If you're stating a fact or something you believe is certain, you use the indicative. If you're expressing an emotion, a wish, doubt, or a necessity, you use the subjunctive. Let's look at when to use each.

When you express a belief or certainty, use the indicative mood. The phrase 'je pense que', meaning 'I think that', introduces something you believe to be true, so the verb that follows is in the indicative. For example, 'Je pense qu’il vient' means 'I think that he is coming'.

Now, let's look at uncertainty. When you negate 'je pense que' to say 'je ne pense pas que', you're expressing doubt, not certainty. This doubt triggers the subjunctive. For example, to say 'I don't think that he is coming', you use the subjunctive form 'vienne': 'Je ne pense pas qu’il vienne'.