In dialectics, a contradiction is formed when two requirements are met:
- Two things must be diametrically opposed
- And one cannot exist without the other
For example: in warfare, attack and defence form a contradiction; without an attack, there is no need for defence (rule 2) and also, defence is the opposite of attack (rule 1).
Note that diametrically opposed does not necessarily mean the literal opposite. The bourgeoisie and proletariat are in contradiction: one cannot exist without the other, and their class interests are diametrically opposed (the bourgeoisie wants to exploit the proletariat, and the proletariat wants to destroy the bourgeoisie as a class so as to liberate themselves).
Contradictions exist everywhere in the world and in many different domains, and it is the solving of contradictions (or the apparition of new ones) that drive change in the general sense of the term, thus dialectics happen.
Chairman Mao Zedong talked at length about contradictions and is a good starting place for theory.
Primary and secondary contradictions
Contradictions are separated into primary and secondary categories. Secondary contradictions are dependent on primary ones, and solving the primary contradiction solves the secondary contradiction.
Some think, for example, that solving class contradictions (moving into communism, a classless society) will also solve several secondary contradictions attached such as: racism, homophobia, sexism, selfishness, etc. This is an example of primary and secondary contradictions. For others, it is impossible to solve secondary contradictions without addressing the primary contradiction.
Solving contradictions
A contradiction is solved when it stops existing; i.e. when both rules stop being applicable.
Thus the proletariat will stop existing as a class when the bourgeoisie stops existing. However, in that scenario, one of two things may happen:
- Another contradiction takes its place
- The contradiction is solved for good
In this example, it means that the proletariat may be replaced by another class -- but inevitably, so will the bourgeoisie (much like how serfs and nobles were replaced by capitalist social classes). Thus another contradiction would take place between these two classes. Or classes could stop existing at all, which would usher in a classless era and solve class contradictions for good (since there are no more classes).