Guided by this law of development, Professor Draper sets out on his task of investigating the course of European progress. For the purpose of facilitating this investigation, he divides the intellectual progress of the nations examined, into five periods: 1, The Age of Credulity; 2, The Age of Inquiry; 3, The Age of Faith; 4, The Age of Reason; 5, The Age of Decrepitude; corresponding with the five divisions of individual life, as previously stated, from infancy to old age. The general line of examination and its results may be stated by giving the opening paragraphs of his closing chapter: 'The object of this book is to impress upon its reader a conviction that civilization does not proceed in an arbitrary manner, or by chance, but that it passes through a determinate succession of stages, and is a development according to law. 'For this purpose we considered the relations between individual and social life, and showed that they are physiologically inseparable from one another, and that the course of communities bears an unmistakable resemblance to the progress of an individual, and that man is the archetype or exemplar of society. 'We then examined the intellectual history of Greece--a nation offering the best and most complete illustration of the life of humanity. From the beginning of its mythology in old Indian legends, and of its philosophy in Ionia, we saw that it passed through phases like those of the individual to its decrepitude and death in Alexandria. 'Then addressing ourselves to the history of Europe, we found that, if suitably divided into groups of ages, these groups, compared with each other in chronological succession, present a striking resemblance to the successive phases of Greek life, and therefore to that which Greek life resembles--that is to say, individual life.' Looking at the successive phases of individual life, Professor Draper finds intellectual advancement to be their chief characteristic. The anatomist discovers that the human form advances to its highest perfection through provisions in its nervous structure for intellectual improvement. In like manner the physiologist ranks the vast series of animals now inhabiting the earth in the order of their intelligence. The geologist declares that there has been an orderly improvement in intellectual power of the beings that have successively inhabited the earth. The sciences, therefore, join with history, infers Professor Draper, in affirming that the great aim of nature is intellectual improvement; intellectual improvement in the individual, and hence, man being the archetype of society, intellectual advancement in the race.