In order to refute Aristotle's theory that free fall speed depends on the quality of the object, Galileo told a simple thought experiment. According to Aristotle, if a light object is tied to a heavy object and then dropped from the tower, the heavy object falls fast and the rope between the two objects is straightened. At this moment, the light object will have a resistance to the heavy one, which will make the falling speed slow. However, on the other hand, the mass of two objects tied together should be greater than that of any single object, and the entire system should fall faster. This contradiction proved Aristotle was wrong. Regardless of the resistance of the air, the speed of all free falls is the same no matter how heavy the matter is.

In the confrontation between old and new theories, science has been continuously progressed. New theories were proved to be truth and the old theories were abandoned. So what is the standard of truth? The ultimate standard of truth is practice, but at the same time there are some alternative standards, including prediction, stability, simpleness and logical unified.

Practical standards mean that theory should be able to guide practice so as to realize people's interests. So the practical standard is pragmatism. Practicality means improving people's interests and social progress. People's interests include the interest of oneself and the others, immediate interests and long-term interests. Newton's theorem can be accepted by everyone, mainly because it is conducive to social practice and played an important role in the industrial revolution.

The interests of man are the criteria for testing truth. Strictly, it should be the experience of interest, that is, I feel I have benefit or suffered, I feel uncomfortable after eating a crab, I feel this car is very good, and so on. So the standard for testing truth is direct experience. No matter how much the engineer said about many high-tech used in a car, it does not fully explain the problem, the ultimate test of truth is the user's feeling. Misunder- standings can cause pain, misdiagnosis by doctors, mis- judgment by judges, mistakes in markets, battlefields, and government decisions can all make people feel pain.

Why should we pursue objective truth? Because countless experiences tell us that objective truth is in our long-term interest. The ultimate essence of all the objective truths we speak of are practical truths. Objectivity is not the ultimate goal of understanding, it is just a means. Deng Xiaoping said, “It doesn't matter whether a cat is black or white as long as it catches mice.” Feyerabend's famous saying is “Anything goes.” There is no absolute right or wrong even between science and religion.  Feyerabend makes sense, but it is wrong to say “Anything goes.” It is wrong to do against the funda- mental interests of the people, and history cannot be reversed. The ultimate criterion for truth is individua