Prior’s Argument (the rough idea)

That which exists or is real is stated unqualifiedly.

To say that something was or will be the case is to qualify it.

To say that something is the case is not to qualify it.

The present is real, but not the past or future.

Broad’s Argument

Time has an order and a sense (intrinsic, or observer-independent, directionality?).

A moving present will not provide for the sense of the temporal order.

Changes in things can be analyzed in terms of having different qualities at different times.

Changes in events can’t.

An event losing the property of being present is like Tom losing being youngest.

An event changing from future to present can’t be explained in this way.

So an event changing from future to present must be explained in terms of Becoming. That is, the past and present exist, but the future does not.