Philosophy,though unable to tell us with certainty what is the true answer to the doubts which it raises,is able to suggest many possibilities which enlarge our thoughts and free them from the tyranny of custom. Thus,while diminishing our feeling of certainty as to what things are,it greatly increases our knowledge as to what they may be.
Source:The Problems of Philosophy, chap. 15（1912).
More info.:http://russell-j.com/R601.HTM