Tonal means physic world, Nagual means fluidity and transformation: ritual practice, dance, ASC's (Altered State of Counciousness), Mysticism. Heterology is closer to Nagual, and that does not mean they as Alterity are outside this world:

"I'm going to tell you about the tonal and the nagual" he said and look at me piercingly. This was the first time in our association that he had used those two terms. I was vaguely familiar with them through the anthropological literature on the cultures of central Mexico. I knew that the tonal (pronounced toh-na'hl) was thought to be a kind of guardian spirit, usually an animal, that a child obtained at birth and with which he had intimate ties for the rest of his life. Nagual (pronounced nah-wa'hl) was the name given to the animal into which sorcerers could allegedly transform themselves, or to the sorcerer that elicited such transformation." (...) "Sorcerers have a special and unique interest in that knowledge. I would say that the tonal and the nagual are in the exclusive realm of men of knowledge." (...) "The tonal is not an animal that guards a person, but a guardian that could be represented as an animal." (..) The tonal is the social person, the organizer of the world, chaos into order organizer : "A guardian is broad-minded and understanding." "A guard on the other hand, is a vigilante, narrow-minded and most of the time despotic." (..) "The tonal is everything we are, everythinig we know, begins at birth and ends at death. "The nagual is the part of us we do not deal with at all, is the part of us for which there is no description -no words, no names, no feelings, no knowledge."

"At the time of birth, and for a while after we are all nagual, the missing tonal give us a feeling of incompleteness, from the moment we become all tonal we do nothing else but to increment that old feeling which accompanies since ancient times and which tell us constantly that there is another part to give us completeness." pp. 122-128.