Why "planet of the apes" but "planet of the blind"?

Question

Why is it *planet of the apes* but *planet of the blind*? Is that "s" necessary after *the ape*? I know that *the* can change singular nouns and adjectives into plural nouns. But is there any rule?

Answer 1

In your examples, both planets are suggested to be in possession by many things (that is, "planet of the apes" could be grammatically rephrased as "the apes' planet"). Blind, like sheep, are irregular plural nouns that do not change their form when made plural. Thus, "Planet of the Blind" indicate that the planet we are naming consists of a significant number of blind individuals who are in charge of the planet. Likewise, "Planet of the Apes" indicates that there are a sigificant number of apes on the planet. "Planet of the Ape" would change the meaning of the title, and perhaps indicate that there is only one great ape who rules the planet.