Suppose that Descartes was having a dream. Could he think in his dream that something was clearly true although it was really false? Could he think in his dream that “I think therefore I am” was...

Suppose that Descartes was having a dream. Could he think in his dream that something was clearly true although it was really false? Could he think in his dream that “I think therefore I am” was clearly true when in fact it was false? Why?