In both the NES and PlayStation versions of Final Fantasy, Intelligence has no effect. This is commonly called the "Intelligence bug" by the community, though strictly speaking no glitches are occurring: there is no line of code in the game that references a character's Intelligence outside of increasing it upon leveling up.
Exactly how Intelligence was meant to function is unclear, but it is generally assumed Intelligence is supposed to be a factor in how much damage or healing a spell will do, as it does in later versions of Final Fantasy. Because Intelligence has no effect in the NES and PlayStation, Red Mage can use Cure just as well as a White Mage. This also means that magic spells never become more powerful, with any given spell being just as powerful when cast by low-level or high-level characters. Combined with the critical hit bug, this results in magic being overall less powerful than physical attacks.
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