Those who are actively engaged in educational pursuits are called upon from time to time to consider the nature of the difficulties in the imparting of knowledge, the psychological impediments that stand in the way of successful instruction. These are many and various; and pertain as well to the givers as to the receivers of learning. This large and well threshed field I have no intention of gleaning once more; I desire simply to draw attention to one form of difficulty on the part of the learner, which has been brought home to me so frequently and at times so forcibly, that I should be inclined to select it as the most salient stumbling-block in the successful acquisition of those branches of study which it falls to my lot to expound. This characteristic, which may be called mental prepossession, is well illustrated in the following narrative, the truth of which, however, is not guaranteed. The story dates from the exciting days when the American public was completely fascinated by the mental gymnastics of the "spelling bee;" and relates that towards the close of a very fierce contest with the alphabet, when only a few stalwart champions remained to encounter the erratic eccentricities of English orthography, the conductor of the "bee" announced with an air of grave importance a word that he felt quite certain would retire not a few of the spelling virtuosi. He then asked their closest attention to his precise pronunciation, and solemnly gave utterance to what for all the world sounded like _cat_. Each hearer attempted to spell this extraordinarily difficult word with a suitably unusual rearrangement of the letters suggested by the sound, and when each effort had in turn been pronounced a failure, the information was given that the correct spelling was _c-a-t_. _Hæc fabula docet_ that when one expects a difficulty he is apt to find it or to make it. Believing the problem to be unusual, he applies unusual methods to its solution; believing it to be complex, he overlooks the simple means by which its mysteries may be unlocked. It matters little how this reputation has come about, whether as the result of personal prejudice or of inherited tradition, whether suggested by the technicality of the subject or the awkwardness of the treatment, whether by the use of a few unusual terms or operations, or by any one of the countless methods, conscious and unconscious, by which such impressions are formed,--the result will be much the same.