Here are some possible answers to the question of what makes life worth living:

1. nothing
2. religion
3. happiness
4. love, work, and play

Evidence from psychology and neuroscience supports the fourth answer. Here's why.

1. Nothing

A few despondent philosophers—such as Nietzsche, Schopenhauer, and David Benatar—have cast doubts on whether life has any intrinsic meaning, and some people are driven to suicide by depression or negative events in their lives. But most people, fortunately, are able to find lots of reason to value their lives, and in surveys most people report themselves as pretty happy. So nihilism may not be a plausible position.

2. Religion

Surveys also indicate that many people report that religion and spirituality are major sources of meaning in their lives. Unfortunately, however, these sources may not be valid, particularly if there is no evidence to support claims for particular religious beliefs. Religious faith may be reassuring, but science cannot objectively tell someone whether they should adhere to Christianity, Islam, Hinduism, or some other religion. It cannot even tell an individual what version of Christianity (Catholic, Baptist, Morman, etc.) or Islam (Shia or Sunni) they ought to adopt. Hence, religion and vague spiritual ideas—such as "everything happens for a reason"—cannot provide an evidence-supported basis for living.

3. Happiness

Psychological research has identified many ways in which people can increase the happiness in their lives, as in Sonja Lyubomirsky's fine book, The How of Happiness. But happiness is usually the result of having a meaningful life, not what makes life worth living in itself. There are people whose lives are meaningful even though they may not be very happy—for example, someone who is struggling with a challenging job while raising a special needs child.

On the other hand, happiness can be cheaply achieved by slacker serenity, a mindless bliss resulting from having minimal goals, access to drugs, or unlimited time for leisure. You can have happiness without much meaning, and meaning without much happiness; thus, happiness is likely not the meaning of life.

4. Love, work, and play

In my new book, The Brain and the Meaning of Life, I argue that these three activities make life worth living. Love includes friendships and family relationships as well as romantic ones. Work includes diverse productive activities, such as community volunteering, in addition to working for wages. Play includes all forms of entertainment such as reading and watching movies, not just games.

Surveys and other psychological studies indicate that love, work, and play do indeed enable people to have lives they value. Neuroscience provides a deeper understanding of how brain processes generate needs for relatedness, autonomy, and competence that can be satisfied by the successful pursuit of love, work, and play. Such satisfaction often yields happiness, but even the pursuit is enough to give life meaning.