Just as we consider three things in the case of a craftsman, namely, the purpose of his work, its model, and the work now produced, so also do we find a threefold word in one who is speaking. There is the word conceived by the intellect, which, in turn, is signified by an exterior vocal word. The former is called the word of the heart, uttered but not vocalized. Then there is that upon which the exterior word is modeled; and this is called the interior word which has an image of the vocal word. Finally, there is the word expressed exteriorly, and this is called the vocal word. Now, just as a craftsman first intends his end, then thinks out the form of his product, and finally brings it into existence, so also, in one who is speaking, the word of the heart comes first, then the word which has an image of the oral word, and, finally, he utters the vocal word.
Thomas Aquinas, De Veritate q. 4 art. 1. (translation from Thomas Aquinas, Truth, vol. 1. Mulligan, tr. Henry Regenery (Chicago: 1952).