The word 反常 is formed by directly combining two conceptual building blocks: 反, meaning to reverse or be opposite to, and 常, meaning the usual, normal, or constant state. By placing them together, the concept is constructed where the first character actively inverts or opposes the fundamental meaning of the second, creating the complete idea of a reversal of what is normal, hence "abnormal" or "unusual". It is a straightforward, ideographic assembly where the relationship is immediately clear, one element negates or flips the other.