The Fallacy of the Second Standard
When making an evaluation, it is important to have a standard of evaluation. A standard enables a rational evaluation because it specifies the method of comparison, and makes the evaluations into facts, instead of opinions. A standard of evaluation is critical to objectivity, since without an objective standard of evaluation, anything goes.
A common fallacy involves the attempted use of two separate standards to form an evaluation. This Fallacy of the Second Standard destroys the attempt at objectivity. By having two or more standards, there will be cases where the standards conflict. At that point, there is no rational method of deciding between the two. The judgment will be based on emotions or moods.
As an example, a man is trying to buy a house. He picks two standards to make his decision by. He chooses cost and size as his criteria. But when he finds that bigger houses cost more, he cannot make a rational decision based on these criteria. He needs to either ignore one of the criteria, or choose a third criteria that bridges between them. He may choose to take the largest house, regardless of the cost. Or he may choose the largest house under $600,000 (a new standard).
A man cannot rationally use two standards of evaluation. If ever confronted with a conflict between them, he must sacrifice one or both. This is true for more than two standards as well. In fact, picking many standards is the equivalent of having no standards at all. Judgments are made by opinions and feelings, and are no longer statements of fact.