Following Brightly's point in the last post, here is a link to a translation of a work by William of Ockham (the other one) that I made some time ago. Not available in English anywhere else, as far as I know. It is all good stuff, but especially interesting in the current context is section 7 ('A probable opinion: affections of the soul are effigies or fictions')
Here Ockham discusses a view he seems to favour. An intention of the soul, or a concept or affection of the soul is nothing other than a predicable or 'subjectible' in a proposition in the mind, to which there corresponds a predicable or subjectible in utterance, and, generally, affections of the soul, whether intentions of the soul or concepts, are propositions in the mind, or syllogisms, or parts of them. These mental terms and propositions are 'effigies' or 'fictions'. They are not true qualities of the mind, and are not real beings existing subjectively in it, but they are certain things thought by the mind whose being is nothing other than being thought. They exist in the sense that a building designed by an architect really exists, which exists in virtue of being designed or made-up, and so does not exist in reality. This made-up thing can also be called an 'intention', because it is not real, and has intentional being, i.e. being thought of in the soul.
The view is not entirely clear. If a thing has being by being thought, is this not a kind of being? But what kind of being? Ockham himself notes the difficulty of supposing that anything can be understood by us, which does not exist in reality, nor any part of it, and which is neither a substance nor a property of anything.