Thomas Hobbes (1588 - 1679), Leviathan (1651)
From part I (spelling slightly updated)
CONCERNING the Thoughts of man, I will consider them first Singly, and afterwards in Train, or dependence upon one another. Singly, they are every one a Representation or Appearance, of some [...]Object. Which Object worketh on the Eyes, Eares, and other parts of man's body; and by diversity of working, produceth diversity of Apparences.
[What is sense?]
The Origin[...] of them all, is that which we call S E N S E; (For there is no conception in a man's mind, which hath not at first, totally, or by parts, been begotten upon the organs of Sense.) The rest are derived from that originals. [...]
The cause of Sense, is the External Body, or Object, which presseth the organ proper to each Sense, either immediately, as in Taste and Touch; or mediately, as in Seeing, Hearing, and Smelling: which pressure, by the mediation of Nerves [...] continued inwards to the Brain, and Heart, causeth there a resistance, or counter-pressure [...]. Which endeavour because Outward, seemeth to be some matter without. And this seeming, or fancy, is that which men call Sense; and consisteth, as to the Eye, in a Light, or Colour figured; To the Eare, in a Sound; To the Nostril, in an Odour; To the Tongue and Palate, in a Savour; And to the rest of the body, in Heat, Cold, Hardness, Softness, and such other qualities, as we discern by Feeling. All which qualities called Sensible, are in the object that causeth them, but so many several motions of the matter, by which it presseth our organs diversly. Neither in us that are pressed, are they anything else, but divers motions, (for motion produceth nothing but motion.) [...] still the object is one thing, the image or fancy is another. So that sense in all cases, is nothing els but origiall fancy, caused (as I have said) by the pressure, that is, by the motion, of externall things upon our Eyes, Eares, and other organs thereunto ordained.
But the Philosophy-schooles, through all the Universities of Christendome, grounded upon certain Texts of Aristotle, teach another doctrine; and say, For the cause of Vision, that the thing seen, sendeth forth on every side a visible species [...] I say not this, as disapproving the use of Universities: but because I am to speak hereafter of their office in a Commonwealth, I must let you see on all occasions by the way, what things would be amended in them; amongst which the frequency of insignificant Speech is one.
[What is imagination?]
[...]When a Body is once in motion, it moveth (unless something els hinder it) eternally; and whatsoever hindreth it, cannot in an instant, but in time, and by degrees quite extinguish it: [...]; so also it happeneth in that motion, which is made in the internal parts of a man, then, when he Sees, Dreams, &c. For after the object is removed, or the eye shut, wee still retain an image of the thing seen, though more obscure than when we see it. And this is it, the Latines call Imagination, from the image made in seeing; and apply the same, though improperly, to all the other senses. [...] IMAGINATION therefore is nothing but decaying sense,[...] So that distance of time, and of place, hath one and the same effect in us. For as at a distance of place, that which wee look at, appears dimme, and without distinction of the smaller parts, and as Voyces grow weak, and inarticulate: so also after great distance of time, our imagination of the Past is weak; and wee lose (for example) of Cities wee have seen, many particular Streets; and of Actions, many particular Circumstances. [...]
[Simple and compound imagination]
Againe, Imagination being only of those things which have been formerly perceived by Sense, either all at once, or by parts at several times; The former, (which is the imagining the whole object, as it was presented to the sense) is simple Imagination; as when one imagineth a man, or horse, which he hath seen before. The other is Compounded; as when from the sight of a man at one time, and of a horse at another, we conceive in our mind a Centaure. [...]
[A theory of emotions]
And seeing dreames are caused by the distemper [= wrong temperature], of some of the inward parts of the Body; divers distempers must needs cause different Dreams. And hence it is, that lying cold breedeth Dreams of Feare, and raiseth the thought and image of some fearful object (the motion from the brain to the inner parts, and from the inner parts to the Brain being reciprocally). And that as Anger causeth heat in some parts of the Body, when we are awake; so when we sleep, the overheating of the same parts causeth Anger, and raiseth up in the brain the Imagination of an Enemy. In the same manner; as naturall kindness, when we are awake causeth desire; and desire makes heat in certain other parts of the body: so also, too much heat in those parts, while wee sleep, raiseth in the brain an imagination of some kindness shewn. In sum, our Dreams are the reverse of our waking Imaginations; The motion when we are awake, beginning at one end; and When we Dream, at another. [...]
From this ignorance of how to distinguish Dreams, and other strong Fancies, from Vision and Sense, did arise the greatest part of the Religion of the Gentiles in time past, [...] and now adayes the opinion that rude people have of Fayries, Ghosts, and Goblins; and of the power of Witches. For as for Witches, I think not that their witchcraft is any real power; but yet that they are justly punished, for the false beliefe they have, that they can do. such mischiefe, joined with their purpose to do it if they can [...]
The Imagination that is raised in man (or any other creature indued with the faculty of imagining) by words, or other voluntary signes, is that we generally call Understanding; and is common to Man and Beast. For a dog [...] will understand the call [...] of his Master; and so will many other Beasts. That Understanding which is peculiar to man, is the Understanding not only his will; but his conceptions and thoughts, by the sequell and contexture of the names of things into Affirmations, Negations, and other formes of Speech. And of this kinde of Understanding I shall speak hereafter.
Of the Consequence or TRAIN of Imaginations
By Consequence, or TRAIN of Thoughts, I understand that succession of one Thought to another, which is called (to distinguish it from Discourse in words) Mental Discourse.
When a man thinketh on any thing whatsoever, His next Thought after, is not altogether so casual as it seems to be. Not every Thought to every Thought succeeds indifferently. But as wee have no Imagination, whereof we have not formerly had Sense, in whole, or in parts; so we have no Transition from one Imagination to another, whereof we never had the like before in our Senses. [...] But because in sense, to one and the same thing perceived, sometimes one thing, sometimes another succeedeth, it comes to passe in time, that in the Imagining of any thing, there is no certainty what we shall Imagine next; Only this is certain, it shall be something that succeeded the same before, at one time or another.
From part IV - a materialist argument?
But to what purpose (may some man say) is such subtilty [as analysis of language and theoretical philosophy] in a work of this nature, where I pretend to nothing but what is necessary to the doctrine of Government and Obedience? It is to this purpose, that men may no longer suffer themselves to be abused,  by [the] doctrine of Separated Essences, built on the Vain Philosophy of Aristotle [...]For it is upon this ground, that when a Man is dead and buried, they say his Soul (that is his Life) can walk separated from his Body, and is seen by night amongst the graves. [...]
Being once fallen into this Error of Separated Essences, they are thereby necessarily involved in many other absurdities that follow it. For seeing they will have these Forms to be reall, they are obliged to assign them some place. But [...] they hold them Incorporeall, without all dimension of' Quantity, and all men know that Place is Dimension, and not to be filled, but by that which is Corporeall; [...] And in particular, of the Essence of a Man, which (they say) is his Soul, they affirm it, to be All of it in his little Finger, and All of it in every other Part (how small soever) of his Body; and yet no more Soul in the Whole Body, than in any one of those Parts. Can any man think that God is served with such absurdities? And yet all this is necessary to believe, to those that will believe the Existence of an incorporeal Soule, Separated from the Body.
And when they come to give account, how an incorporeal Substance can be capable of Pain, and be tormented in the fire of Hell, or Purgatory, they have nothing at all to answer, but that it cannot be known how fire can burn Souls.
 Again, whereas Motion is change of Place, and Incorporeall Substances are not capable of Place, they are troubled to make it seem possible, how a Soul can goe hence, without the Body to Heaven, Hell, or Purgatory; and how the Ghosts of men (and I may add of their clothes which they appear in) can walk by night in Churches, Churchyards, and other places of Sepulture. To which I know not what they can answer [...]back
The entire "Leviathan" is available on the internet at Oregon State University: http://osu.orst.edu/instruct/phl302/texts/hobbes/ghindex.html(University of Oregon)