As mentioned before, the most effective solutions are achieved when an inventor solves a technical problem that contains a contradiction. When and where does a contradiction occur?

 It occurs when we are trying to improve one characteristic, or parameter, of a technical system and cause another characteristic, or parameter, of the system to deteriorate. A compromise solution is then usually considered. A technical system has several characteristics (parameters) — weight, size, color, speed, rigidity, and so on. These characteristics describe the physical state of a technical system. When solving technical problems, these characteristics help determine the technical contradiction residing in the system.

Increasing the power of an engine (positive improvement) requires an increase in the size of the engine (negative effect). So, an inventor considers increasing the power partially in order to reduce the negative effect (compromise solution). To increase the speed of an airplane, a new and more powerful engine is installed. This increases the weight of the airplane so the wings can no longer support it during takeoff. Increasing the wing size produces more drag, slowing the airplane down. These are some examples of how improvements can produce contradictions. The improvement goals were never fully achieved because the root technical contradictions were never resolved. These are called technical contradictions because they happen inside of technical systems. The 40 Principles are used to resolve technical contradictions.

There is another type of contradiction — physical contradiction — appearing when two opposite properties are required from the same element of a technical system or from the technical system itself. There are different methods for resolving physical contradictions (separation of contradictory requirements in time or space, changing the physical state of a substance, separation upon condition).