To doubt is to suspend judgment. It is to say not know something either to be true or not true. To seek that which is without doubt is almost impossible.
Descartes thought that he knew the thinker to be true. That the thinker is reflecting on his thinking cannot be doubted. This, I believe, is wrong. For it is not the thinker but the perceiver, observer. although in the first instance of experience, there are objects, but no subject (observer). It is only later that the observer notices itself as an observer.
Descartes made the mistake of assuming we notice ourselves from the beginning. A child does not know its own reflection in the mirror. A dog chases its tail mistakenly taking it as something else not belonging to its body.
This navigation to an awareness of self (subject) occurs only after awareness of others (object or external objects).
The epistemological sequence is of knowing, first, other, then self, not the other way around as Descartes had thought. This is what I mean by pronouncing “there are things”. Observation of others comes before observation (noticing) of self.