User:BFD1/Frege's puzzle

Frege's Puzzle is a thought exercise devised by Gottlob Frege which is meant to illustrate a distinction between the sense and reference of a thought. In the puzzle, Frege asks the reader to consider two sentences:
 * (1) The Evening Star is the Morning Star (a=b)
 * (2) The Evening Star is the Evening Star (a=a)

The terms "Evening Star" and "Morning Star" both have the same reference, namely the planet Jupiter. They are thus referentially equivalent, in that both terms pick out the same object in the world. However, the puzzle is meant to show that although both sentences appeal to the same reference, sentence (1) seems to say something informative about the world, while sentence (2) is trivially true&mdash;or true by definition&mdash;and thus seems less informative. Thus, Frege's puzzle was to understand how the two sentences can have the same reference and yet possess different "cognitive values".

Frege's solution to the puzzle was to make a distinction between the sense and the reference of an idea (or thought, or sentence).