Meliorism

One can read about it in the works of Lester Frank Ward, William James, and John Dewey.

For James,[2] meliorism stands in the middle between optimism and pessimism, and treats the salvation of the world as a probability rather than a certainty or impossibility.

A closely related concept discussed by Jean-Jacques Rousseau and Marquis de Condorcet is that of perfectibility of man.

Condorcet's statement, "Such is the object of the work I have undertaken; the result of which will be to show, from reasoning and from facts, that no bounds have been fixed to the improvement of the human faculties; that the perfectibility of man is absolutely indefinite; that the progress of this perfectibility, henceforth above the control of every power that would impede it, has no other limit than the duration of the globe upon which nature has placed us.

"[7] Like William James before him Rosling held a halfway position between optimism and pessimism that emphasized humanity's capacity to improve their world.