Mozi's philosophical thought reflects the duality of the small working class liberated from patriarchal slavery. The reasonable factors in his thought were inherited and developed by later materialist thinkers, and the dross of his mysticism was absorbed and utilized by theologians after Qin and Han Dynasties. Mozi, as the founder of mohists in pre-Qin Dynasty, had a great influence in the history of China philosophy.

In addition, Mozi's achievements and contributions in the field of science and technology are various, mainly including:

1. Cosmology

Mozi believes that the universe is a continuous whole, and individuals or parts separated from this unified whole are all components of this unified whole. In other words, the whole contains individuals, and the whole is composed of individuals, and there is an inevitable organic connection between the whole and the individuals. Starting from this continuous view of the universe, Mozi further established a theory about time and space. He named time "Jiu" and space "Yu", and gave the definitions of "Jiu" and "Yu", that is, "Jiu" refers to all time in ancient and modern times, and "Yu" refers to all spaces in east, west, north and south, and time and space are continuous. After giving the definitions of time and space, Mozi further discussed whether time and space are finite or infinite. He thinks that time and space are limited. For the whole, time and space are infinite, while for some people, time and space are poor. He also pointed out that continuous space-time is composed of space-time elements. He defined the elements of time and space as "beginning" and "end". "Start" is the smallest unit of time and "End" is the smallest unit of space. In this way, space-time is continuous and infinite, and this continuous and infinite space-time is composed of the smallest units. There is finiteness in infinity and discontinuous space-time theory in continuity.

On the basis of space-time theory, Mozi established his own theory of motion. He unified and linked time, space and object motion. He believes that in the continuous and unified universe, the movement of objects is manifested in time differences and spatial position migration. Without the change of time series and position distance, there is no movement, no simple movement in time and space.

Mozi also expounded the origin and attributes of matter incisively. Among the pre-Qin philosophers, Laozi first proposed that the origin of matter is "born from nothing" (Laozi's chapter 1) and "everything is born from something, and everything is born from nothing" (Laozi's chapter 40). Mozi first opposed this view of Laozi and put forward the idea that everything begins with "being". He pointed out that there are two kinds of "nothingness". One is that there was something in the past and there is nothing now. For example, an extinct bird cannot be denied as "existence" because it no longer exists. One is that things that have never happened, such as the sky were to fall, are nonexistent "nothingness". Things that didn't exist originally won't give birth to "you", and things that existed originally and then didn't exist are not "you" born from "nothing". It can be seen that "you" exists objectively. Then, Mozi further elaborated the issue of material attributes. He believes that if there is no stone, you won't know the hardness and color of the stone, and if there is no sun and fire, you won't know the heat. In other words, without physical objects, attributes do not exist, and attributes are an objective reflection of physical objects. The reason why people can perceive the properties of matter is because there are physical objects.

2. Mathematics

Mozi was the first scientist in the history of China to treat mathematical problems rationally. He gave a series of propositions and definitions of mathematical concepts, which are highly abstract and rigorous.

The mathematical concepts given by Mozi mainly include:

On the definition of "times". Mozi said, "Double is two." (The Book of Mohism) That is, the original number is added once, or the original number is multiplied twice, which is called "times". For example, two feet is "times" one foot. On the definition of "Ping". Mozi said, "The level is the same as the height." (The Book of Mohism) is the same height, which is called "Ping". This has the same meaning as Euclid's geometric theorem that "the common vertical lines between parallel lines are equal".

Regarding the definition of "the same length", Mozi said: "the same length, the same positive phase." (On the Book of Mohism) That is to say, the lengths of two objects are exactly one-to-one correspondence and completely equal, which is called "equal length".

On the definition of "zhong". Mozi said, "China people are of the same length." (On the Book of Mohism) The "middle" here refers to the symmetrical center of the object, that is, the center of the object is a point with the same distance from the surface of the object.

About the definition of "artificial intelligence". Mozi said, "Hey, a China person is as long." The word "er" here is a circle. Mozi pointed out that the circle can be drawn with compasses or checked with compasses. Compasses have been widely used before Mozi, but it is Mozi's contribution to give a precise definition of circle. Mozi's definition of circle is exactly the same as that in Euclid's Geometry.

On the definition of a square. Mozi said that all four corners are right angles, and a quadrilateral with four equal sides is a square. You can draw a square with the "moment" of a square ruler and test it.

This also accords with the definition of square in Euclid geometry.

On the definition of straight line. Mozi said that the three-point line is a straight line. As the definition of straight line, three-point * * * line is widely used to measure the height and distance of objects in later generations. Liu Hui, a mathematician in the Jin Dynasty, used three-point * * * lines to measure the height and distance in the monograph Calculation of Islands. After the Han Dynasty, the "Mountain Sight" on the crossbow machine was invented accordingly.

In addition, Mozi also discussed the decimal numerical system. China widely used decimal notation as early as Shang Dynasty, and Mozi was the first scientist to summarize and expound the concept of value system. He clearly pointed out that different digits have different values. For example, on the same number, one is less than five, while on different numbers, one can be greater than five. This is because in the same number (unit, tens, hundreds, thousands, etc.), five contains one, and when one is in a higher number, it in turn contains the invention of decimal, which is a great contribution of China to world civilization. As Needham said in the Mathematical Volume of the History of Science and Technology in China, "The number system of Shang Dynasty is more advanced and scientific than that of ancient Babylon and ancient Egypt at the same time", "Without this decimal system, it is almost impossible to have our unified world now".

3. Physical properties

Mozi's research on physics involves many branches such as mechanics, optics and acoustics, and gives many definitions of physical concepts, makes many important discoveries and summarizes some important physical theorems.

First of all, Mozi gave the definition of force and said, "Force, punishment (form) is also exciting." In other words, force is the cause of the motion of an object, even though the function of the motion of an object is called force. In this regard, he cited an example to illustrate that this is like lifting heavy objects from bottom to top, and it can only be done because of its powerful function. At the same time, Mozi pointed out that when an object is stressed, it will also produce a reaction force. For example, after two objects of equal mass collide, they will move in opposite directions. If the mass of two objects is very different, the object with large mass will not move after collision, but the reaction force still exists.

Then, Mozi gave the definitions of "moving" and "stopping". He thinks that "moving" is because of pushing, and more importantly, he puts forward "stop, it will take a long time, so there is no time to stop." The point of view is that the stop of object motion comes from the action of resistance and impedance. If there is no resistance, the object will move forever. This view is regarded as the pioneer of Newton's law of inertia, which is more than 1000 years longer than the whole world at the same time, and it is also the symbol of the birth and development of physics (Aristotle thinks that force is the reason for making objects move, and without force, objects will not move, but stopping is the nature of objects, which is in line with the results observed by ordinary people, but superficial and wrong).

Mozi also made an incisive statement about the lever theorem. He pointed out that the reason why the balance beam will balance when weighing heavy objects is that the "mark" is short and the "mark" is long. In modern scientific language, "Ben" is a heavy arm, "Biao" is a force arm, and the mechanical formula is force × force arm (Biao) = weight × force arm (Ben). Now people are generally used to calling lever theorem Archimedes theorem. In fact, Mozi put forward the lever theorem 200 years earlier than Archimedes, so it is fair to call it Mozi theorem. In addition, Mozi also made a series of studies on mechanical problems such as lever, inclined plane, center of gravity and rolling friction. I won't go into details here. In the history of optics, Mozi was the first scientist to conduct optical experiments and systematically study geometric optics. If Mozi laid the foundation of geometric optics, it is not an exaggeration, at least in China. As Needham said in China's History of Science and Technology, Physics Volume, Mozi's research on optics was "earlier than Greek as we know it" and "not as good as Indian".

Mozi first discussed the relationship between light and shadow. He carefully observed the changing law of moving objects and put forward the proposition that "the scenery does not move". That is to say, when a moving object looks at its shadow from the table, it is also moving with the object. Actually, this is an illusion. Because when the position of a moving object moves, the image it formed a moment ago has disappeared, and the image formed after its displacement is newly formed, rather than the original image moving to a new position. If the original image does not disappear, it will always exist in its original position, which is impossible. Therefore, the movement of the seen image is only formed by the continuous and uninterrupted life and death of the old and new images with the movement of the object, not the movement of the image itself. Mozi's proposition was later inherited by famous artists, which put forward the proposition that "the bird's shadow has not moved"

Later, Mozi also discussed the umbra and secondary shadow of objects. He pointed out that if the light source is not a point light source, the object will produce umbra and auxiliary shadow because of the repeated irradiation of light from each point; If the light source is a point light source, only the umbra appears.

Then, Mozi conducted pinhole imaging experiments. He clearly pointed out that light travels in a straight line, and the image formed by an object through a small hole is an inverted image. This is because when light passes through an object and then through a small hole, the upper part of the object is imaged at the bottom and the lower part of the object is imaged at the top due to the straight-line propagation of light, so the image formed is inverted. He also discussed the relationship between the size of the image and the tilt of the object and the distance from the light source, pointing out that the shadow is long and thin when the object is tilted or the light source is far away, and short and thick when the object is straight or the light source is near. If it is reflected light, a shadow is formed between the object and the light source.

What is particularly valuable is that Mozi systematically studied plane mirror, concave mirror and convex mirror, and obtained a series of basic principles of geometric optics. He pointed out that the images formed by flat mirrors are the same size, far and near are symmetrical, but left and right are reversed. If two or more flat mirrors illuminate each other, repeated reflections will occur, forming countless images. Concave mirror's imaging is to form a positive image in the middle. The positive image at a distance from the middle is larger, the positive image at a distance from the middle is smaller, and the positive image in the middle is as big as the object. Outside the "middle", the image is upside down, the near "middle" image is large, and the far "middle" image is small. The convex mirror only forms a positive image, with a large near mirror image and a small far mirror image. The center here is the center of the spherical mirror. Although Mozi has always been unable to distinguish between center and focus, and confused them, his conclusion is basically consistent with the imaging principle of modern spherical mirrors.

Mozi also studied the propagation of sound and found that wells and poppies can amplify sound and use it skillfully. He once taught students that when guarding the city, in order to prevent the enemy from digging tunnels to attack the city, they should dig a well every 30 feet, put a big poppy in the well, put thin cowhide on the mouth of the poppy, and let people with good hearing lie on the poppy to listen, so as to know whether the enemy is digging tunnels and where the tunnels are dug, and make preparations to guard against the enemy.

4. Mechanical manufacturing

Mozi is a master of mechanical manufacturing, and his talent and attainments in this field were fully demonstrated in the offensive and defensive drills that Chu defeated Song Dynasty. It took him three years to develop a flying wooden bird. He is also an expert in making vehicles, and he can build a car with a load of 30 stones in less than one day. The car he built was fast, labor-saving and durable, which was appreciated by people at that time.

It is worth pointing out that Mozi almost knew all about the manufacturing technology of various weapons, machinery and engineering buildings at that time, and he had many creations. In Mozi, he introduced and expounded in detail the suspended door structure of the city gate, the structure of various defense facilities inside and outside the city gate, the manufacturing technology of crossbows, oranges and various offensive and defensive equipment, and waterways. These instruments and facilities he talked about have a great influence on the military activities of later generations.

5. Philosophical aspects

The most outstanding philosophical achievements of Mozi are epistemology and logic, and his contribution is incomparable to other philosophers in pre-Qin period.

Mozi believes that people's sources of knowledge can be divided into three aspects, namely, listening, speaking and knowing relatives. He divided what he heard into hearsay and hearsay, but in Mozi's view, the Ministry should not simply accept both hearsay and hearsay, but must digest and integrate them to make them its own knowledge. Therefore, he stressed the need to "smell and get its meaning", that is, after listening and accepting, we should think and investigate on the basis of other people's knowledge, and then inherit and carry forward.

Mozi's "knowledge" contains the meaning of reasoning and investigation, and refers to the knowledge obtained through reasoning. He particularly emphasized "knowing what it is but not knowing why", that is, unknown knowledge can be inferred from known knowledge. If the fire is known to be hot, it is inferred that all fires are hot; Compasses can draw circles, and it is inferred that all circles can be measured with compasses. It can be seen that Mozi's knowledge and learning are not passively and simply accepted, but contain a positive and enterprising spirit.

In addition to listening and speaking knowledge, Mozi attached great importance to personal understanding, which is also a big difference between Mozi and other pre-Qin philosophers. Mozi's intimate knowledge is the knowledge he has gained through his own experience. He divided the intimate process into three steps: consideration, connection and understanding. "Trouble" is the state of people's cognitive ability to seek knowledge, that is, the beginning of the mind, interested in the mind and seeking something. But you may not get knowledge just by thinking. For example, if you look at a foreign object with your eyes open, you may not be able to identify the real image of the foreign object. Therefore, it is necessary to "receive" knowledge, so that sensory organs such as eyes, ears, nose, tongue and body can contact with foreign objects and perceive the external nature and shape of foreign objects. However, the "received" knowledge is still very incomplete knowledge, and only superficial knowledge of things can be obtained. Some things, such as time, are not felt by the senses. Therefore, the knowledge acquired by human senses is still preliminary and incomplete, and it is necessary to integrate, sort out, analyze and infer the acquired knowledge in order to reach a "clear" knowledge realm. In a word, Mozi organically links the three aspects of knowledge sources and is unique in the field of epistemology.

Mozi was also the founder of China's logic. He called logic "debate" and regarded it as the thinking law of "distinguishing similarities and differences, distinguishing right from wrong". In his view, people use thinking to understand reality and make judgments that are nothing more than "the same" or "different", "yes" or "no". To this end, we must first establish a rule to distinguish similarities and differences, right and wrong, and use this as a standard to measure and judge. If it is "yes", it is "no" if it is not. This judgment is "indispensable". People use thinking to understand things, and the judgment of the same thing is either "yes" or "no" There is no third possibility, it can't be both "yes" and "no", and it can't be both "yes" and "no" or both. In modern logical terms, this is law of excluded middle's law of harmony and non-contradiction.

Based on this law of thinking, Mozi further established a series of thinking methods. He summed up the basic thinking method as "sketching the nature of all things and discussing the ratio of word groups." Give examples, express ideas in words, and tell the reasons. Take by class, give by class "("small take "). That is to say, the purpose of thinking is to explore the inevitable connection between objective things, and to explore the form of reflecting this inevitable connection, expressed by "name" (concept), "word" (judgment) and "saying" (reasoning). Take by class, give by class ",which is equivalent to the analogy of modern logic, is an important reasoning method. In addition, Mozi also summed up a variety of reasoning methods, such as hypothesis, outspoken, choice of words, deduction, induction and so on. Mozi's argument has formed an orderly and systematic system, which is unique in the ancient world, alongside ancient Greek logic and ancient Indian hermeneutics.

6. Military aspects

The most famous books about guarding city tactics in China's ancient war are Mozi and Fifteen Volumes of Mozi, of which fourteen volumes and fifteen volumes introduce the equipment, tactics and key points of guarding city, with a total of twenty articles, eleven of which are for the city gate, for high altitude, for ladders, for water and for emergencies. The tactics of guarding the city in Mozi are very rich, and the other eleven articles cover almost all siege techniques in the cold weapon era.

To sum up, we can see Mozi's profound scientific attainments and great achievements. He was one of the outstanding scientists in ancient China. Regrettably, Mozi's rational light in the field of science and technology almost went out with the decline of Mohism. Most scientists in later generations paid attention to practicality and neglected rational exploration, which was a great loss in the history of science and technology in China.