Someone skilled in dialectical idealism: someone able to arrive at historical conclusions through consideration of contradictions.
Someone skilled in dialectical materialism: someone able to arrive at socio-political conclusions through consideration of class differences.
Someone knowledgable about dialects.
Someone skilled in dialectics: someone able to arrive at logical conclusions through reasoned argument.
An intellectual, such as a philosopher or theologian.
One who spends time thinking, contemplating or meditating.
A poser; a conundrum that requires some thinking.
The brain; the mind.