Words are the thought of ages crystallized, or rather embodied with a constantly growing soul. The word 'Progress', like the word 'Humanity', is one of the most significant. It is a Latin word, not used in its current abstract sense until after the Roman incorporation of the Mediterranean world. It contains Greek thought summed up and applied by Roman minds. Many of the earlier Greek thinkers, Xenophanes and Empedocles as well as Plato and Aristotle, had thought and spoken of a steady process in things, including man himself, from lower to higher forms; but the first writer who expounds the notion with sufficient breadth of view and sufficiently accurate and concrete observation to provide a preliminary sketch, was the great Roman poet who attributed all the best that was in him to the Greeks and yet has given us a highly original picture of the upward tendency of the world and of human society upon it. He, too, so far as one can discover, was the first to use the word 'progress' in the sense of our inquiry. The passage in Lucretius at the end of his fifth book on the Nature of Things is so true and brilliant and anticipates so many points in later thought that it is worth quoting at some length, and the poet's close relation with Cicero, the typical Greco-Roman thinker, gives his ideas the more weight as an historical document. He begins by describing a struggle for existence in which the less well-adapted creatures died off, those who wanted either the power to protect themselves or the means of adapting themselves to the purposes of man. In this stage, however, man was a hardier creature than he afterwards became. He lived like the beasts of the field and was ignorant of tillage or fire or clothes or houses. He had no laws or government or marriage, and though he did not fear the dark, he feared the real danger of fiercer beasts. Men often died a miserable death, but not in multitudes on a single day as they do now by battle or shipwreck. The next stage sees huts and skins and fire which softened their bodies, and marriage and the ties of family which softened their tempers. And tribes began to make treaties of alliance with other tribes. Speech arose from the need which all creatures feel to exercise their natural powers, just as the calf will butt before his horns protrude. Men began to apply different sounds to denote different things, just as brute beasts will do to express different passions, as any one must have noticed in the cases of dogs and horses and birds. No one man set out to invent speech. Fire was first learnt from lightning and the friction of trees, and cooking from the softening and ripening of things by the sun.