Free from extraneous elements
Posing no difficulty
Without addition, decoration, or qualification
Not elaborate or showy, as in appearance or style
Having only a limited ability to learn and understand
Free from guile, cunning, or deceit
Of little distinction
One deficient in judgment and good sense
It's as simple as that.
Surely he had a simple checkbook file.
I loved to sound him on the various reforms of the day, and he never failed to look at them in the most simple and practical light.
A simple yes or no would suffice.
Surely his vocabulary included such a simple word.