Enough has been said to show that the Progress of humanity belongs to the same order of ideas as Providence or personal immortality. It is true or it is false, and like them it cannot be proved either true or false. Belief in it is an act of faith. The idea of human Progress then is a theory which involves a synthesis of the past and a prophecy of the future. It is based on an interpretation of history which regards men as slowly advancing--pedetemtim progredientes--in a definite and desirable direction, and infers that this progress will continue indefinitely. And it implies that, as The issue of the earth's great business, a condition of general happiness will ultimately be enjoyed, which will justify the whole process of civilisation; for otherwise the direction would not be desirable. There is also a further implication. The process must be the necessary outcome of the psychical and social nature of man; it must not be at the mercy of any external will; otherwise there would be no guarantee of its continuance and its issue, and the idea of Progress would lapse into the idea of Providence. As time is the very condition of the possibility of Progress, it is obvious that the idea would be valueless if there were any cogent reasons for supposing that the time at the disposal of humanity is likely to reach a limit in the near future. If there were good cause for believing that the earth would be uninhabitable in A.D. 2000 or 2100 the doctrine of Progress would lose its meaning and would automatically disappear. It would be a delicate question to decide what is the minimum period of time which must be assured to man for his future development, in order that Progress should possess value and appeal to the emotions. The recorded history of civilisation covers 6000 years or so, and if we take this as a measure of our conceptions of time-distances, we might assume that if we were sure of a period ten times as long ahead of us the idea of Progress would not lose its power of appeal. Sixty thousand years of HISTORICAL time, when we survey the changes which have come to pass in six thousand, opens to the imagination a range vast enough to seem almost endless. This psychological question, however, need not be decided. For science assures us that the stability of the present conditions of the solar system is certified for many myriads of years to come. Whatever gradual modifications of climate there may be, the planet will not cease to support life for a period which transcends and flouts all efforts of imagination. In short, the POSSIBILITY of Progress is guaranteed by the high probability, based on astro-physical science, of an immense time to progress in.