Good and Bad, in the sense in which the words are here intended (which is, I believe, their usual sense), are ideas which everybody, or almost everybody, possesses. These ideas are apparently among those which form the simplest concstituents of our more complex ideas, and are therefore incapable of being analysed or built up out of other simpler ideas. When people ask What do you mean by good? the answer must consist, not in a verbal definition such as could be given if one were asked What do you mean by pentagon? but in such a characterization as shall call up the appropriate idea to the mind of the questioner. This characterization may, and probably will, itself contain the idea of good, which would be a fault in a definition, but is harmless when our purpose is merely to stimulate the imagination to the production of the idea which is intended. It is in this way that children are taught the names of colours; they are shown (say) a red book, and told that that is red; and for fear they should think red means book, they are shown also a red flower, a red ball, and so on, and told that these are all red. Thus the idea of redness is conveyed to their minds, although it is quite impossible to analyse redness or to find constituents which compose it. (§ 4 ¶ 1)

In the case of good, the process is more difficult, both because goodness is not perceived by the senses, like redness, and because there is less agreement as to the things that are good than as to the things that are red. This is perhaps one reason that has led people to think that the notion of good could be analysed into some other notion, such as pleasure or object of desire. A second reason, probably more potent, is the common confusion that makes people think they cannot understand an idea unless they can define it—forgetting that ideas are defined by other ideas, which must be already understood if the definition is to convey any meaning. When people begin to philosophize, they seem to make a point of forgetting everything familiar and ordinary; otherwise their acquaintance with redness or any other colour might show them how an idea can be intelligible where definition, in the sense of analysis, is impossible. (§ 4 ¶ 2)