It appears now that ideas may be distinguished into three kinds:  first, Ideas derived from original perceptions, properly termed ideas of memory; second, Ideas communicated by language or other signs; and third, Ideas of imagination.  These ideas differ from each other in many respects; but chiefly in respect to their proceeding from different causes.  The first kind is derived from real existences that have been objects of our senses; language is the cause of the second, or any other sign that has the same power with language; and a man’s imagination is to himself the cause of the third.  It is scarce [ly] necessary to add, that an idea, originally of imagination, being conveyed to others by language or any other vehicle, becomes in their mind an idea of the second kind; and again, that an idea of this kind, being afterwards recalled to the mind, becomes in that circumstance an idea of memory.”—­El. of Crit., Vol. ii, p. 384.

5.  Whether, or how far, language is to the mind itself the instrument of thought, is a question of great importance in the philosophy of both.  Our literature contains occasional assertions bearing upon this point, but I know of no full or able discussion of it.[30] Cardell’s instructions proceed upon the supposition, that neither the reason of men, nor even that of superior intelligences, can ever operate independently of words.  “Speech,” says he, “is to the mind what action is to animal bodies.  Its improvement is the improvement of our intellectual nature, and a duty to God who gave it.”—­Essay on Language, p. 3.  Again:  “An attentive investigation will show, that there is no way in which the individual mind can, within itself, to any extent, combine its ideas, but by the intervention of words.  Every process of the reasoning powers, beyond the immediate perception of sensible objects, depends on the structure of speech; and, in a great degree, according to the excellence of this chief instrument of all mental operations, will be the means of personal improvement, of the social transmission of thought, and the elevation of national character.  From this, it may be laid down as a broad principle, that no individual can make great advances in intellectual improvement, beyond the bounds of a ready-formed language, as the necessary means of his progress.”—­Ib., p. 9.  These positions might easily be offset by contrary speculations of minds of equal rank; but I submit them to the reader, with the single suggestion, that the author is not remarkable for that sobriety of judgement which gives weight to opinions.