"Positive emotion can be about the past, the present, or the future. The positive emotions about the future include optimism, hope, faith, and trust. Those about the present include joy, ecstasy, calm, zest, ebullience, pleasure, and (most importantly) flow; these emotions are what most people usually mean when they casually-but much too narrowly-talk about "happiness." The positive emotions about the past include satisfaction, contentment, fulfillment, pride, and serenity.
It is crucial to understand that these three senses of emotion are different and are not necessarily tightly linked. While it is desirable to be happy in all three senses, this does not always happen. It is possible to be proud and satisfied about the past, for example, but to be sour in the present and pessimistic about the future. Similarly, it is possible to have many pleasures in the present, but be bitter about the past and hopeless about the future. By learning about each of the three different kinds of happiness, you can move your emotions in a positive direction by changing how you feel about your past, how you think about the future, and how you experience the present."
- Martin E. P. Seligman