There are two ways by which we usually acquire knowledge:--The one is by _observation_, without the use of language, and which is common to us with those who are born deaf and dumb; and the other is _through the medium of words_, either heard or read. In both cases, however, the knowledge retained consists entirely of the several _ideas_ which the objects or the words convey; and what we are now to shew, is, that these ideas thus conveyed, can neither be received by the mind, nor retained by the memory, till they have undergone this process of "reiteration." While, on the contrary, it will be seen that, whenever this process really takes place, the idea thus reiterated does become part of our knowledge, and is, according to circumstances, more or less permanently fixed upon the memory. We shall for this purpose endeavour to trace the operation of the principle, both in the case of ideas communicated by objects without language, and in those conveyed to the mind by means of words. That this act of reiteration of an idea by the mind, must take place, before objects of perception can become part of our knowledge, will, we think, be obvious, from a consideration of the following facts.--When, for example, we are in a crowded room, or in the fields, numerous sounds enter the ear,--thousands of images enter into and impress the eye, yet not one of these becomes part of our knowledge till it is _thought of_;--that is, till the idea suggested by the sensation, has not only been perceived, but reiterated by the mind. This will appear to many so plain, that any farther illustration of the fact may be deemed useless. But experience, has shewn, that the illustration of this important process in education, is not only expedient, but is really necessary; as the overlooking of this simple principle has often been the cause of great inconsistencies on the part of teachers. We shall therefore endeavour to exhibit the working of the principle in various forms, that it may be fully appreciated when we come to apply it.