Mechanistic view

Biological basis

While a person's overall happiness is not objectively measurable, this does not mean it does not have a real physiological component. The neurotransmitter dopamine, perhaps especially in the mesolimbic pathway projecting from the midbrain to structures such as the nucleus accumbens, is involved in desire and seems often related to pleasure. Pleasure can be induced artificially with drugs, perhaps most directly with opiates such as morphine, with activity on mu-opioid receptors. There are neural opioid systems that make and release the brain's own opioids, active at these receptors. Mu-opioid neural systems are complexly interrelated with the mesolimbic dopamine system. New science, using genetically altered mice, including ones deficient in dopamine or in mu-opioid receptors, is beginning to tease apart the functions of dopamine and mu-opioid systems, which some scientists (e.g., Kent C. Berridge) think are more directly related to happiness. Stefan Klein in his book "The Science of Happiness" links these biological foundations of happiness to the concepts and findings of Positive Psychology and Social Psychology.

Difficulties in defining internal experiences

It is probably impossible to objectively define happiness as humans know and understand it, as internal experiences are subjective by nature. Because of this, explaining happiness as experienced by one individual is as pointless as trying to define the color green such that a completely color blind person could understand the experience of seeing green. While one can not objectively express the difference between greenness and redness, it is possible to explain the physical phenomena that cause green to be observed, the capacities of the human visual system to distinguish between light of different wavelengths, and so on. Likewise, the following sections do not attempt to describe the internal sensation of happiness, but instead concentrate on defining its logical basis. It is therefore important to avoid circular definitions -- for instance, defining happiness as "a good feeling", while "good" is defined as being "something which causes happiness".