- lism, humanism, and evolutionism. Moreover, the objecti- vity of truth cannot be fully confirmed. All truths must be subjective. Any truth may be overturned in the future. We can only improve the objectivity of the knowledge through practice. That is, the standard of objectivity is the practical standard.

Practicality is the fundamental standard of truth, but this standard is often not easy to use. It is difficult to make timely and accurate assessments of the long-term benefits of people and social progress. To determine which theory is practical, some alternative criteria are needed. Predictability is not only in the interest of people, but also in accordance with the principle of evolution. It is the main difference between science, art, and religion. Therefore, predictability is a substitute standard of truth.

One hundred successful explanations are not as good as a successful prediction. Galileo predicted that objects of different qualities fall at the same speed and it was confirmed by experiments on the Leaning Tower of Pisa. This successful prediction overthrew Aristotle's theory. Einstein opposed the Newtonian system by using the theory of relativity. At the beginning, no one believe it. In May 1919, Eddington's observation of solar eclipse found that the light did bend in the gravitational field. This new experience immediately convinced everyone of Einstein's theory.

Predictability does not confirm a theory. One or two successful predictions may be lucky like a blind cat encounter a dead rat, even many successful predictions do not indicate that a theory can always succeed. Proof of truth is often not accomplished in one go, especially for those important truths and long-term careers that often require constant reflection and verification. No standard tells us how many success can confirm a truth. It depends entirely on people's choices with comparison of different theories.

After an error occurs in the theory, it will not necessarily be immediately overturned, it can often be repaired. But the need for repair means that the theory is unstable. If a theory always changes, it will be hard to convince people. The viewpoint of movement is of course correct, but the idea of static metaphysics cannot be completely denied, because theory must have stability, and it is best to use eternal, universal truth. Even if the theory is not so stable, it should be as stable as possible and should not change every day. When an experimental phenomenon is confirmed in many people's experiments, it is relatively stable and we treat it as truth.

The original meaning of metaphysics refers to abstract theories and was later regarded by Marxism as a static, isolated, one-sided theory that is opposed to dialectics. But this idea of Marxism is wrong because people study abstract theories in order to seek constant things among changes. Therefore, the idea of being static is not a reactionary point of view, but an indispensable point of view required by practice.