Osric Ilien and I were discussing sorcerers and their intuitive understanding of magic vs. the wizards' learned paths.

If Spellcraft is the "practical" understanding and use of magic, as opposed to the theory and lore of Kn: Arcana, then why not use a spellcaster's primary ability score (Int, Wis, or Cha) as the ability modifier for the skill?

I imagine sorcerers and bards understanding their magic as a power within them that they need only learn to express and shape it. That's how I imagine charisma working with their magic. A very internal, intuitive understanding.

Wizards hold the traditional course of lore and scholarship. They spend a great deal of time with books and generally long apprenticeships under a master - a formulaic approach would be the norm, and Intelligence seems to cover memory and problem solving, but not the creative spontaneity of a charismatic sorcerer or bard.

And Wisdom can apply to nearly any mental task, as there are broad interpretations of the ability. Wisdom might represent the enlightened acceptance of a monk or the devoted faith of a priest, but either way a cleric would understand magic through that lense. Shrewd perception is a powerful tool for understanding magic, and faith is equally potent in the ability to believe it will happen, or to know through a sort of divine inspiration.

Ultimately, the reasoning is that every spellcaster and their classes can have extremely different ways to make their magic work, and to understand other kinds of magic. Each has some valid, believable precepts. To each their own.