The following obligations are demandable at once, except*1 pointone with resolutory conditionone with suspensive conditionone whose performance does not depend upon a future or uncertain eventsone whose performance does not depend upon a past event unknown to the parties

The obligation that is not demandable at once is the one with a suspensive condition.

Here's why:

1. An obligation with a resolutory condition is demandable at once because the obligation is valid until the resolutory condition occurs.

2. An obligation whose performance does not depend upon a future or uncertain event is demandable at once because there's no condition preventing the obligation from being fulfilled immediately.

3. An obligation whose performance does not depend upon a past event unknown to the parties is demandable at once because the fulfillment of the obligation does not hinge on an unknown past event.

4. However, an obligation with a suspensive condition is not demandable at once. A suspensive condition is a condition that suspends the obligation until the condition is fulfilled. Therefore, until the suspensive condition occurs, the obligation cannot be demanded.