The idea “I think, therefore I am” seems to say: if (1) the activity of thinking is going on, then (2) a thing must exist that is doing the thinking. Does (2) really follow from (1)? Can an activity...

The idea “I think, therefore I am” seems to say: if (1) the activity of thinking is going on, then (2) a thing must exist that is doing the thinking. Does (2) really follow from (1)? Can an activity exist by itself even if nothing is “doing” that activity? Why?