Under every great political, social, religious, and educational movement, there are found certain truths or principles that act as motive power. The movement may be very complex and varied in its manifestations, but the underlying truths or principles are generally clear and simple. The Protestant Reformation of the sixteenth century, for example, with all the civil and ecclesiastical disturbances it brought about, was based on these two well-known principles: 1. Men are saved by faith alone; and 2. The Bible is the only rule of faith and practice in religion. The American Revolution, with all its multiplicity of events, was founded on the principle that taxation without representation is tyranny. Illustrations might be multiplied indefinitely; but the truth will hardly be questioned that great movements in society generally derive their impulse from one or more principles which admit of perspicuous statement.