Self-determination and happiness
Dryden asserts that happiness stems from self-determination—being able to "call today [one's] own" and being able to say that one "ha[s] lived today" and "had [one's] hour." The pleasure in having taken control of one's own life is enough for one to gather the will to go on and enjoy life even in the face of misfortune: "Be fair or foul or rain or shine, / The joys I have possessed, in spite of fate, are mine."
Temporality
Dryden makes reference to the past, present, and future over the course of the poem. The poem argues that a man should "call today his own" and "live today," showing a determination to live in the moment and take control of present circumstance. This, in turn, will make whatever the future has in store—whether pleasant or unpleasant—more bearable: "Tomorrow do thy worst, for I have lived today. / Be fair or foul or rain or shine, / The joys I have possessed, in spite of fate, are mine." Not even Heaven has control over the past, and "what has been, has been"; one will always have one's past pleasures and successes, and the less pleasant circumstances of the past are over with now. Thus, overall, the poem aims to take control over the past and future by focusing on the present, and showing how a steady attitude can bring calmness—whatever has happened in the past, and whatever may happen in the future.
Fate and control over circumstance
Three main parties appear in the poem: the individual, fate, and Heaven. The individual is happy when they are the one with primary control over their own circumstances, and having that control—even temporarily—can help them cope with negative circumstances outside of their control. Fate can bring good or bad circumstances into the individual's life, but it cannot change past joys and successes. In fact, according to Dryden, not even Heaven can exercise control over the past. Thus, neither the fate, Heaven, nor the individual control past circumstances. The individual is assumed to have self-determination and the ability to change and/or act within their present circumstances; the future is left mostly up to fate; and Heaven is looked to as having ultimate control over circumstances and happenings.
