A running theme in fantasy literature is True Names – each thing (or at least person) has a true name, and knowing the true name of a thing gives you power over it. But why’s that? Here’s my theory. If you use a normal word for a thing, the word has connotations and shades of meaning that distract you from the thing itself. Thus, the use of carefully-crafted “true names”, words which exist to be directly mapped to the thing itself without connotations, puns, and other distractions.
Given this, consider the implications of aphasia. My theory is that an aphasic wizard would be incredibly powerful as long as he couldn’t remember words, because when he was unable to think of the word “cat”, it would turn out that “pointy-eared fuzzy tail thing” would be an exact invocation of the thing itself.
The neat thing is that this has awesome narrative properties; the more stressful and panicked he is, the more powerful he is.