The Metaphysics of Becoming a Tree

All magic systems imply some ontology, and most of the European ontologies come from Aristotle's view of the world. This is why someone turned into stone might retain their vision, motion, and thoughts.

In Aristotle's view, everything has:

• form (the shape)
• substance (what it's made out of)
• telos (what it's for)
• first-cause (where it came from)

For example:

• Rain forms drops, is made out of water, it's for watering plants, and it comes from the sky.
• People have people-shapes; flesh, sinew and bone constitute their bodies; people exist to praise the gods and achieve glory; and mothers provide the first cause.
• Fireballs have rain-drop shape but fire for substance, they exist to burn, and come from angry wizards.

Anyone transformed to stone would retain their organs with the same telos, meaning that a liver would continue to process toxins, and the eyes continue to see, because that's what eyes are for (regardless of their 'substantive cause' (meaning, the substance they are made from).

Similarly, when a spell makes someone big, they wouldn't have problems with vision, their lungs won't collapse, and they won't suffer any back-pain, because they are the same as they were, except for the size, which is simply a larger version of their original form, with more substance added via the magic of the growth spell.

If none of that makes sense, blame Aristotle.

Of course, we won't find a one-to-one match with magic systems and Ancient Greek thought. I suspect this is just how people think. A series of interviews with children have shown that younger children tend to explain events in terms of teliology - that lakes form because animals need to drink (rather than gravity and the natural depression of the earth). Aristotle seems to have expressed some view, inherent to humanity.