This difference of intention, and remission of the mind in thinking, with a great variety of degrees between earnest study and very near minding nothing at all, every one, I think, has experimented in himself.  Trace it a little further, and you find the mind in sleep retired as it were from the senses, and out of the reach of those motions made on the organs of sense, which at other times produce very vivid and sensible ideas.  I need not, for this, instance in those who sleep out whole stormy nights, without hearing the thunder, or seeing the lightning, or feeling the shaking of the house, which are sensible enough to those who are waking.  But in this retirement of the mind from the senses, it often retains a yet more loose and incoherent manner of thinking, which we call dreaming.  And, last of all, sound sleep closes the scene quite, and puts an end to all appearances.  This, I think almost every one has experience of in himself, and his own observation without difficulty leads him thus far.  That which I would further conclude from hence is, that since the mind can sensibly put on, at several times, several degrees of thinking, and be sometimes, even in a waking man, so remiss, as to have thoughts dim and obscure to that degree that they are very little removed from none at all; and at last, in the dark retirements of sound sleep, loses the sight perfectly of all ideas whatsoever:  since, I say, this is evidently so in matter of fact and constant experience, I ask whether it be not probable, that thinking is the action and not the essence of the soul?  Since the operations of agents will easily admit of intention and remission:  but the essences of things are not conceived capable of any such variation.  But this by the by.

CHAPTER XX.

Of modes of pleasure and pain.

1.  Pleasure and Pain, simple Ideas.

Amongst the simple ideas which we receive both from sensation and reflection, pain and pleasure are two very considerable ones.  For as in the body there is sensation barely in itself, or accompanied with pain or pleasure, so the thought or perception of the mind is simply so, or else accompanied also with pleasure or pain, delight or trouble, call it how you please.  These, like other simple ideas, cannot be described, nor their names defined; the way of knowing them is, as of the simple ideas of the senses, only by experience.  For, to define them by the presence of good or evil, is no otherwise to make them known to us than by making us reflect on what we feel in ourselves, upon the several and various operations of good and evil upon our minds, as they are differently applied to or considered by us.

2.  Good and evil, what.