While the change in philosophical thinking is very real, it is not really out of step with the past. Locke said that we experience particular things. This is not always clear from his descriptions of experience. Remember that Aristotle said that the mind, that part of the soul that thinks, is nothing until it begins to think. It does not exist as an entity of itself until it thinks of itself. What Locke said was that the mind is a blank slate, that it contains no ideas, until it experiences. Aristotle's concept of experience is through imagination. Imagination is the image producing mechanism in the body that produces images of what the senses detect in the world around us. The mind, in order to image those thinks it is contemplating or remembering, uses Imagination to produce those images. Descartes' description follows Aristotle's very closely particularly when he said that the mind imagines while at the same time making imagination a part of the body. When, In An Essay Concerning Human Understanding, Locke began with the assumption that everything we know we know only from experience, what he was saying is that ideas are only derived from experience and the mind can not operate without ideas.

Locke's theory of knowledge begins with his definition of Ideas as anything that existed in the mind that could be expressed through words. Experience, as he described it, is ultimately derived from only two sources, simple ideas created by our interaction with sensible qualities in things of the sensible world, and simple ideas developed out of our observations concerning the operations of our mind. Locke, although he made a number remarks concerning them, did not explain how it was that sensations excite ideas in the mind. He only stated that God produced in us the capacity for doing so. What Locke called "qualities" are those characteristics of objects which cause ideas in our mind through sensation. There are two kinds of qualities in objects. Primary, or real, qualities are those that always exist in an object. These would include solidity, extension, figure, number, and motion or rest. They are always connected with the object whether we sense them or not. Secondary, or imputed, qualities consist of combinations of several primary qualities where we do not recognize these primary qualities distinctly. When we sense particular things, for example, we sense along with them a quality of unity and though the primary qualities are there what we perceive is not them but the object itself. For example, we may sense a certain texture, a particular form, a specific animal odor. These would be simple ideas formed by primary qualities. We may also sense a leather chair, which would be a simple idea produced by secondary qualities. But if we were to analyze the idea of a leather chair into its constituent qualities of feel, form, and sense, that would constitute a set of complex ideas developed by the mind out of the simple ideas formed through sense. Perception is the immediate occasion of an idea previously formed by judgment that has been activated by sensation. Thus, when someone recognizes the full extent of an object known from past judgments at the moment of the sensation of the object.

This concept of particular objects forming simple ideas and of perceptions being always of actual things bothered many who otherwise followed Locke's train of thought. But we must remember that immediate perception is more than just a philosophical notion. A prehistoric man facing a charging saber-toothed tiger, or a modern man facing a careening out of control automobile both have the same problem. They must react immediately. There is no time for judgment. The mind is simply too slow. If man did not have the capability of immediate action without mental consideration, he would have been extinct long ago. Descartes made that ability a basic part of his description of the relation between sense and action, saying that animal spirits can directly initiate action. This is one of the shortcomings of the more idealistic empiricism of both Berkeley and Hume as we will presently discover. As Locke explained perception, it is an immediate connection between sensation and a pre-established judgment. The judgment must already exist, having been developed through previous experience. Then and only then can the mind arrive at the perception. This makes sense if you consider that the first time you experience something it takes a period of time before you realize exactly what it is you have perceived. It has an advantage over Descartes in that by including in the description elements formed from previous experience, it illustrates its dependence on both experience and learning.

The beginning of our treatment of things in our sensual world, Aristotle said, is through naming them. Locke has taken the stand that the things we are dealing with mentally are not the things that we sense, but the ideas that are formed in our minds by what we sense.

The use of words then being to stand as outward marks of our internal ideas, and those ideas being taken from particular things, if every particular idea that we take in should have a distinct name, names must be endless. To prevent this, the mind makes the particular ideas received from particular objects to become general; which is done by considering them as they are in the mind such appearances--separate from all other existences, and circumstances of real existence, as time, place, or any other concomitant ideas. This is called abstraction, whereby ideas taken from particular beings become general representatives of all of the same kind; and their names general names, applicable to whatever exists conformable to such abstract ideas.

One of the major criticisms of Locke's theory of knowledge deals with his statement that we can know not only space but also immense and perhaps infinite space through experience. But consider along this line that part of our experience includes the simple ideas of individual objects, each as a unity of simple sensations which are of themselves only confusedly sensed. The analysis of these simple ideas will result in complex ideas of the constituent elements. In other words the simple ideas of animal odor, specific form, and feel or texture are determined of their own accord. But the feel, odor, and forms of leather chairs are complex ideas developed through reflection and abstraction from the simple idea of a leather chair. Thus distance or length is a part of the unity of a simple object, when reflected on, it becomes a component of a class of objects, such as leather chairs. Once extracted from the complex idea of leather chairs, it becomes something of its own. Though it is no longer dependent on experience, it could not have been developed outside of experience. But there is nothing unusual about expanding the limit of a complex idea created out of simple ideas in the mind to such ideas as immensity or infinity. It is just that such ideas since they were formed in the mind and not developed directly from experience are abstract.

However, in order for our minds to operate on even simple ideas it must first name them. At the same time he said that names are determined by public agreement. This is necessary because he assumed the only purpose of language to be communication. Public agreement, of course, entails a necessarily public language. However, since words are symbols for ideas and ideas are not communicable, they exist only in the mind, they are symbols for what is necessarily private. It would seem, however, that if language is necessarily public then it must exist first before we can name simple ideas and subsequently before we develop any complex ideas. To make matters worse, since we deal almost exclusively in abstract ideas, the exact nature of anyone's internal ideas can never be determined. As a result, a complex language must exist before knowledge of the external world can even be approximated. This is a fascinating problem, but one which neither Locke, nor any subsequent philosopher has attempted to solve.