James-Lange Theory of Emotion was posed by both James and Lang at approximately the same time (hence the name James-Lange) and suggests emotions are a consequence of our physiological responses to external stimuli followed by identification of the emotion by examining the physical responses.
So, some external stimulus produces a physiological response in your body. Then, you examine this physiological response and identify the emotion you are experiencing based on the physiological response. For example, you see a bear in the woods, and you begin to tremble. You then identify the fact that you are trembling and conclude that you are afraid…”I am trembling, therefore I am afraid.”