I’m not really feeling like defending St. Thomas’ description in this topic, I just wanted to comment on a misunderstanding. The general process St. Thomas and his commentators John of St. Thomas and Cajetan is as follows (simplified and streamlined):
External Senses > Inner Senses, i.e. common sense and imagination / phantasm (the “mental picture”) > Active Intellect abstracting the form from the material conditions of the phantasm > Impressed intellect receiving the form > Expressed Intellect “speaking” the word/concept insofar as the knower has the same form as the object in an intelligible manner
By speaking we don’t mean a train of thought or having our language words in our mind, it just means the intellect expresses the concept as a formal similitude to the object.
Edit: And that’s just the general manner of encountering and knowing a thing. I didn’t really speak to recall and reflection or any number of other specifics.
Edit 2: The key point for St. Thomas’ realism is that the concept and the object, while under different modes of existence, are constituted by the same form, and that the concept (outside of reflection) isn’t the object of thought but the medium by which we know the external object, that which contains the intellible content of the object, in a sense, in a psychic way as opposed to its natural way.