system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: why is, "goodnight," one word, but, "good morning," two words?
gpt
I am quite certain that the explanation goes like this: "Good night" is a phrase composed of two words. Even if "Goodnight" has become acceptable, this is only due to widespread use and repetition of incorrect usage. This incorrect usage, alternatively, can also answer your question.