I think there is a point in life where one realizes that one can be critical. So I would have to say that to some degree that initial intellect is entirely uncritically synthesizing.
There is an age before language truly adheres (up to, on average, 18 months) when there is little evidence that negation applies to infants. Experiences can be positive or negative, but only as they are biologically so. To the extent language works, before that, it seems to be entirely operant conditioning without symbolic content. Memory works in terms of the evocative function of the hind-brain but without the calming-and-resolving intervention of the frontal cortex.
Evidence for this phenomenon come from studies of early memory, where people find that experiences before that cutoff can generally not be considered analytically, and cognitive approaches to addressing their effects backfire, because invoking them either negatively or positively has the same effect.
If this frontal function really does, as it appears, start development at a given age (instead of developing more continuously, sneaking on and only getting noticed at a certain point) then before that, I would say one cannot be critical or analytic, and we all have the experience somewhere of an entirely synthetic world.