'I do not see how God could be understood to be anything but a deceiver if
these ideas [that sense gives us] were transmitted by a source other than corporeal
things. It follows that corporeal things exist.'
Meditation 6.
We can't think of God as a deceiver. We believe that the source of our sense experience is a rich configuration of ordinary objects populating a world which is external to our thinking. If this belief were wrong, we would have to believe that God was misleading us. If S/he was misleading us, S/he would be a deceiver. Therefore we are not mislead and the source of our sense experience is: objects in the external world.
God is not a deceiver
We believe external objects cause our sense experience
If we were wrong about this, our Creator would have to bear responsibility for
deceiving us.
Therefore we are not wrong and external objects exist.