Incognizable

Because Tom just woke up, his speech is incognizable.

Source: tatoeba (9982499)

1658, Thomas Saintserf (translator), Entertainments of the Cours: or, Academical Conversations, compiled by Melchior de Marmet, London, p. 104, A dead Body is always incognizable, not only because it is ordinarily changed, but because it neither speaks, nor acts; and for that the qualities of its Soul, which we should know, are departed with her, and have left nothing but a trunk, and a lump without motion.

Source: wiktionary

The lettish race […] was not a primitive stock, as the finnish, the germanic, or slavonian, but a distinct branch, now become incognizable, of the Slavi […]

Source: wiktionary

[…] if therefore position is, to the nascent intelligence, incognizable except as the position of something that produces an impression on the organism; how is it possible for the idea of position ever to be dissociated from that of body?

Source: wiktionary