Circular thinking is a logical fallacy.
"Whatever is less dense than water will float, because whatever is less dense than water will float" sounds stupid, but "Whatever is less dense than water will float, because such objects won't sink in water" might pass.
"Circular reasoning is often of the form: "a is true because b is true; b is true because a is true." Circularity can be difficult to detect if it involves a longer chain of propositions."
http://en.wikipedia.org/wiki/Circular_reasoning
"Whatever is less dense than water will float, because whatever is less dense than water will float" sounds stupid, but "Whatever is less dense than water will float, because such objects won't sink in water" might pass.
"Circular reasoning is often of the form: "a is true because b is true; b is true because a is true." Circularity can be difficult to detect if it involves a longer chain of propositions."
http://en.wikipedia.org/wiki/Circular_reasoning
