ciples. Those deductions of fitness to au end or purpose, which constitute princi ple, certainly cannot be made till after the requisite propositiops have been present ed or have occurred to the mind. Pre viously to this, the conscious being may be said to possess the capacity to perceive and to deduce relations ; and it seems of very little consequence whether we call this capacity innate or not.
We are so constituted, that most of our sensations give us either pleasure or pain; and whenever these are vivid, we are put into a situation of mind, respecting them, called desire; namely, for the continuance or return of the pleasurable sensations, and for the cessation or absence of those that are painful. These desires, in their various modifications and combinations, are distinguished by the general name of the passions. Whenever they are strong and urgent, they engage the mind so fully, that the ordinary association of ideas, and the regular processes of reason, become obscured, interrupted, or suspended. A continuance of this state, as when the passions are exalted by disease, is called insanity : and in all states of passion man is more or less insane.
None of our sensations are simple, and consequently none of our ideas can be so. All sensations consist of parts, represent ing parts of the objects perceived,whether contemporaneously or in succession; and we are also capable of receiving two or more sensations at the same time. Whe ther the difference between one sensation and another may arise merely from the re lations of their own parts with respect to each other, or from any other causes, is not of importance to be discussed in this place ; but it is certain that we are great ly interested in observing these relations. Thus we take notice, that one thing is greater or less than another ; that in figure, position, duration, and other af fections, they are not the same ; and that certain changes in inanimate, as well as in conscious beings, are, without excep tion, followed by other changes, from which we are led to expect and to foretel events. This last class of observations establishes the doctrine of causes and effects and a large part of our lives is employed in determining the order of these successions.
Among numerous other inaccuracies whiQh tend to mislead in the investigation of ideaology, a principal one is, that the term idea has been confounded with that of notion. Notions always grow out of the relations of ideas, and they always imply comparison. When the notion or thing asserted agrees with the ideas or events, (which are ideas considered in succession) it constitutes truth; if other wise, it is falshood.
Our sensations in every case, without exception, afford no more than a partial indication of the nature of the objects which cause them. We cannot see the
whole of an animal, but only one side, and that very imperfectly; so that the ordinary visible perception of a horse would be the same, whether its hair were long or short, its eyes imperfect or the contrary, &c. and the recollection, or idea, of that individual horse would be still more im perfect, by the omission of particular variations or spots of colour, or other subordinate objects ; which, though they may have existed in the sensation, have not remained in the memory. Thus it is, from the nature of things, that some part of the sensations will be abstracted, or ieft out in the idea; and if, in *easoning upon that subject, namely, the horse, a comparison were to be instituted between that animal and a cow, the attributes they have in common would, in some cases,be alone attended to, and in others form the chief object of consideration. In this manner, arbitrarily, or rather from the necessity of the case, we constantly direct our inquiries to abstract ideas, (which are more or less defective, when general ly considered) instead of attending to the individuals, as we must always do in the sensations; that is to say, when we ob serve and make experiments. And from these obvious truths we may see how it is that we acquire notions of genera, species and individuals; how the first elements of language are formed by ab straction ; how difficult it is to reason from sensations or experiments, by the use of ideas, which are their, necessarily imperfect, representatives; and how easy it is for us to mislead ourselves, and others, by paralogism, in the use of gene ral propositions, if we do not constantly adhere to the same degrees of abstrac tion, or if we do not, in all practical ap plications, again introduce the abstracted parts, which, though we may have reject ed them (like numbers in algebra) for the facility of our mental process, must in variably be resumed, whenever the thea tre of nature or society is to be again en tered.
These are the principal outlines of the science which treats of ideas, or the ma terials of our knowledge, and the conduct of mind, in the disposition and treatment of them. Most writers have treated this subject either loosely and without order, or, by running into divisions upon dif ferences, not of primary importance in the nature of things, have confused the various parts into which it most extensively branches. Hence it is that we hear of ideas of sensation and reflection; complex ideas of modes, substances, and relations; ideas distinct, confused, real, fantastical, adequate, inadequate, true, and false. See LANGUAGE, also UNDERSTANDING.