On the Use of Language as a Sign of Rationality

Here is a paper on the difference between the use of language by human beings and what appears to be the use of language by apes:

Dennis Bonnette, A Philosophical Critical Analysis of Recent Ape-Language Studies.

See also:

Walker Percy, Lost in the Cosmos: The Last Self-Help Book.

Idem, The Message in the Bottle: How Queer Man is, How Queer Language Is, and What One Has to Do With the Other.

Robert Sokolowski, Phenomenology of the Human Person.

The last book has not yet been released, but I was fortunate enough to take a graduate class with Msgr. Sokolowski where we used an earlier draft of it as our text.

Further references on the topic would be appreciated.