Energy independence" and its rhetorical (修辭的) companion "energy security" are, however, slippery concepts that are rarely though through.

Albert Einstein predicted this in 1905, when he introduced the concept of relative time as part of his Special Theory of Relativity.

It is based on the concept of positive thinking.

In schools, teachers and pupils alike often assume that if a concept has been easy to learn, then the lesson has been successful.

It will change the concept of food.