Complex sentence: In the 18th century Enlightenment common sense came to be frequently seen as the basis for modern thinking, and contrasted to metaphysics, which was associated with the "ancien régime".
Split into simpler sentences: In the 18th century Enlightenment common sense made a come-back and came to be seen as the basis for modern thinking. It was contrasted to metaphysics, which was associated with the "ancien régime".