A dream is a certain disposition of sleeping people, in which the forms and imagined likenesses of various things are impressed upon the minds of the sleepers. They arise many ways, as Gregory [Moralia 5.31 or 22] and Macrobius say about the Somnium Scipionis .  On account of the linking and union of the soul with the flesh, sometimes dispositions and emotions arising from the body resound in the mind itself, because of this attachment of the flesh to the soul. Therefore in dreaming we often intuit the images of such things we are accustomed to see with some frequency while awake.

Again, in the same place [at chapter 14 he says that] in dreams we see the likenesses of things, of species and bodies, and not the things themselves.   Though it is the species of things we see while dreaming, we call them by the names of these things, and soley on the basis of the likeness we attribute [to these image the properties] of these things. When we are awake, we comprehend the forms of things with our senses, but when we are asleep we intuit the images of things with our  spirit.

original latin

"Cum spiritus bonus in hac visa spiritum humanum assumit aut rapit, non est dubitandum, illas imagines visas esse rerum aliquarum, quas nosse utile est. Dei enim munus est." Consimiles autem imagines aliquando operatur angelus sathanae, qui se transfigurat in angelum lucis, "ut cum illi in manifestis bonis creditum sit, seducat ad sua."  Sed quando huiusmodi somnia fiant per revelationem, iudicat sobrius intellectus, quando divinitus per gratiam est adjutus. Somniis itaque non est passim fides adhibenda, nec omnino simpliciter respuenda, cum aliquando certa habeatur de futuris divinitus per somnia coniectura.

Somnia itaque indifferentia causantur aliquando ex complexione, ut sanguineus somniat laeta, melancholicus tristia, cholericus ignea, phlegmaticus, pluvias, nives et aquatica, et cetera huiusmodi, quae uniuscuiusque conveniunt complexioni, sexui et aetati, ut dicit Constantinus.

Aliquando ex appetitu et affectione, ut famelicus somniat de cibo, ebrius, sitiens, de potu, et de eius contrario, quanto autem talis plus somniat bibere vel comedere, tanto expergefactus, vehementius esurire se reperit vel sitire. Aliquando ex vehementi studio et mentis circa aliquid applicatione, ut avarus semper somniat autem, semper videtur qui[d] computet pecuniam, vel quod augeat vel diminuat argentum suum.

Aliquando ex cerebri perturbatione, ut patet in dispositis ad phrenesim et maniam, qui mira somniant et inaudita, secundum enim vaporem cellulam phantasticam inficientem vel immutantem, ipsa somnia immutantur. Aliquando ex sanguinis infectione, qui enim corruptum habent sanguinem, somniant se ambulare per loca immunda, corruptionem habentia et foetorem. Aliquando ex aeris immutatione, aer enim ad immutationem dispositus, corpus immutat ad eandem immutationem.