Common responses to this paradox resort to logic and semantics.
- Logic: if such a thing as an irresistible force exists, then no object is immovable, and vice versa. It is logically impossible to have these two entities (a force that cannot be resisted and an object that cannot be moved by any force) in the same universe.
- Semantics: if there is such a thing as an irresistible force, then the phrase immovable object is meaningless in that context, and vice versa, and the issue amounts to the same thing as asking, e.g., for a triangle that has four sides.
This paradox is a form of the omnipotence paradox, but that paradox is most often discussed in the context of God's omnipotence (Can God create a stone so heavy that He cannot lift it?).
The paradox should be understood as an exercise in logic, not as the postulation of a possible reality. According to modern scientific understanding, there are not and indeed cannot be either irresistible forces or immovable objects. An immovable object would have to have infinite inertia and therefore infinite mass. Such an object would collapse under its own gravity and create a singularity. An irresistible force would imply an infinite energy, which by Albert Einstein's equation E = mc² is equivalent to an infinite mass. Note that, in the modern view, a cannonball which cannot be deflected and a wall which cannot be knocked down are both types of the same (impossible) object: an object with infinite inertia.
An example of this paradox in non-western thought can be found in the origin of the Chinese word for paradox (Chinese: 矛盾; pinyin: máodùn; literally "Spear-Shield"). This term originates from a story (see the Kanbun example) in the 3rd century BC philosophical book Han Feizi.[1]. In the story, a man was trying to sell a spear and a shield. When asked how good his spear was, he said that his spear could pierce any shield. Then, when asked how good his shield was, he said that it could defend from all spear attacks. Then one person asked him what would happen if he were to take his spear to strike his shield; the seller could not answer. This led to the idiom of "zìxīang máodùn" (自相矛盾), or "self-contradictory".