Even Heraclitus said that everything in the world determines the law of the struggle of opposites. Any phenomenon or process testifies to this. Acting simultaneously, opposites create a state of tension. He defines what is called the internal harmony of a thing.
The Greek philosopher illustrates this thesis with an example of the bow. The bowstring pulls together the ends of this weapon, preventing them from dispersing. Thus, mutual tension gives rise to higher integrity. Thus, the law of unity and opposition is realized. He, according to Heraclitus, is universal, forms the core of true justice and is a condition for the existence of an ordered Cosmos.
The philosophy of dialectics believes that the law of unity and struggle of opposites is the fundamental foundation of reality. That is, all objects, things and phenomena have within themselves certain contradictions. It can be trends, some forces that are fighting among themselves and at the same time interact. Dialectical philosophy offers to clarify this principle to consider the categories that specify it. First of all, this is identity, that is, the equality of a thing or phenomenon to itself.
Two varieties of this category can be distinguished. The first is the identity of one thing, and the second is their whole group. The law of unity and struggle of opposites is manifested here in the fact that objects are a symbiosis of equality and difference. They interact, giving rise to movement. In any particular phenomenon, identity and difference are opposites that cause one another. Hegel defined this philosophically, calling their interaction a contradiction.
Our very ideas about the source of development come from the recognition that everything that exists is not integrity. It has self-contradiction. The law of unity and struggle of opposites is thus manifested as a similar interaction. Thus, Hegel’s dialectical philosophy sees the source of movement and development in thought, and the materialistic followers of the German theoretician found it also in nature, and, of course, in society. Quite often, two definitions can be found in the literature on this subject. It is a "driving force" and a "source of development." They are usually distinguished from each other. If we are talking about immediate, internal contradictions, then they are called the source of development. If we are talking about external, secondary reasons, then we have in mind the driving forces.
The law of unity and struggle of opposites also reflects the instability of the existing balance. Everything that exists changes and undergoes various processes. In the course of this development, it acquires a special specificity. Therefore, the contradictions are also unstable. In philosophical literature, it is customary to distinguish four main forms. Identity-difference as a kind of embryonic form of any contradiction. Then comes the time for change. Then the difference begins to form as something more expressive. Further, it turns into a significant modification. And, finally, it becomes the opposite of where the process began - non-identity. From the point of view of dialectical philosophy, such forms of contradictions are characteristic of any development process.