Mark Rowlands (really the argument was given by another philosopher, Georg Lichtenberg, in the 18th century), argues: "Perhaps there are just thoughts, and no person to whom the thoughts attach." Perhaps, that is, there are 'ownerless' thoughts. This may be understood in at least two ways. First of all, there may be a bundle of thoughts, but no mind that has the bundle. Secondly, there may not even be a bundle of thoughts, but just 'free-floating' thoughts, and no mind. Note that the argument is not that this is the case. The argument is only that this might be the case. The argument is only that "Perhaps" there is no mind. That is all that is needed to undermine Descartes' 'cogito ergo sum' ('I think, therefore I am').
However, this argument can in turn be countered with the argument that it is simply not possible for thoughts to exist without minds (or souls) having them. Thoughts, on this argument, are the acts of minds. If there is no mind, there is no act of the mind, i.e. no thought. Hence we could argue as follows:
(1) If a thought exists, then a mind exists.
(2) A thought exists.
———> A mind exists.
However, Descartes wants to argue not merely that some thought or other exists, and hence, that some mind or other exists. He wants to argue that the thought that exists is his thought, and hence, that his mind exists.
(1) A thought exists.
(2) If a thought exists, then a mind exists.
(3) The thought that exists is a thought of my mind.