Up to the present, pleasure and pain have been studied first separately, as two perfectly distinct states, pure, by hypothesis, from every admixture. We then examined those singular cases where pain becomes the material or occasion of pleasure, and _vice versâ_. We have still to speak of those cases where the agreeable and the painful _coexist_ in varying proportions in the consciousness—_e.g._, in the mountain-climber who feels at the same time fatigue, the fear of the precipices, the beauty of the landscape, and the pleasure of difficulty vanquished. Nothing is more frequent than these mixed forms; they would even be the rule if one could admit, with certain authors, that there are no unmixed pleasures or pains; but by their complex and composite nature they are, in fact, emotions, and we shall come to them again later on. The subject of this chapter is quite different. It is the much-discussed, still unsolved, and perhaps insoluble problem of neutral states, states of indifference, free from any accompaniment, either pleasurable or painful. Do such exist? Both the affirmative and negative are maintained by good authorities; there is even a psychologist who seems to me to have adopted each thesis in turn.[53] Footnote 53: For a short historical summary of the question up to the middle of the nineteenth century, see Bouillier, _Du plaisir et de la douleur_, chap. xi. The question can only be entered on in two ways—by observation and by argument. Let us examine the results of these two methods. 1. Does the state of indifference exist as an _observable fact_? Bain is, among contemporary writers, the principal champion of this thesis, which has excited a lengthy discussion.[54] He does not pretend to affirm that there is a single state of feeling free from every agreeable or disagreeable element; but if these elements only exist as infinitesimal quantities, psychology need take no account of them. Pleasure and pain are clearly defined generic states; yet there is a practical interest in knowing whether any neutral conditions exist. Bain finds the type of these in cases of simple excitement, which may be accompanied either by pleasure or by pain, but remain distinct from either. The sensation of burning, the smell of asafœtida, the taste of aloes, these are modes of excitement which we call pain, because in them pain predominates. The noise of a mill, the confused murmur of a great city, are modes of excitement which may be called agreeable or disagreeable; but the excitement is the essential fact, the pleasure and pain are accidental. Footnote 54: See _Mind_, Oct. 1887, Jan. and April 1888, Jan. 1889; and J. Sully, _The Human Mind_, vol. ii. pp. 4, 5.