 Thus the meanings of sentences are not simply derivable from the meanings of the words in them, and the meanings of those words are not derivable from the “impressions” to which they refer. When children begin to speak, they utter “sentences” that, though short (Mommy!) are whole, complete, and meaningful expressions. It is only when they learn to read that they realize sentences are composed of individual words. Over time, the sentences increase in decomplexity, as people participate in the activities of life. As adults, people speak a vast variety of highly decomplex expressions—including, for example, those involved in the practice of a science, or a religion.