Thinking is a function of the mind.
The mind is a component of our seamlessly integrated trinity manifestation of spirituality: heart, mind and soul.
The mind's "job" is to relate the outside world (that which is outside our skin) as an object (objects) to our heart (wherein resides the orientation of our "I am" experience).
The mind is also the locus container of language, and language is our abstract relational device to each other.
So I find it interesting that Descartes would, in effect, base a confimation of being upon his relationship, not just with the world outside our skin, but with other people perhaps specifically.
Was he, perhaps without realizing it, in effect also implying that without each other, we are nothing!?