Descаrtes’ discussiоn оf dreаms cаn be read as cоntaining the following argument: 1. If I am certain that I am now sitting before the fire, in my dressing gown, with paper in my hands, and so on, then I am certain that I am not now dreaming. 2. I am not certain that I am not now dreaming. So, I am not certain that I am now sitting before the fire, in my dressing gown, with paper in my hands, and so on. Put this way, is the argument valid?