Vitality, defined as the ability to live, grow, and evolve, distinguishes living from non-living entities and represents a core psychological motivation. Authors such as Bernarr Macfadden viewed it as an energy that can be nurtured, highlighting physical and mental strength through effort, while T.
Troward associated it with spiritual growth, claiming that its development requires increased intelligence and power. John Harvey Kellogg described vitality as a mysterious "life force" that animates organisms, and Lilian Whiting linked it to spiritual mastery over the body. These viewpoints highlight vitality’s dual nature—as both a biological necessity and a philosophical quest for life’s essential dynamism.