“I want to be free,” seventeen-year-old Sylvia Plath declared in a letter to her mother — a yearning that hurled her in the inevitable logical direction of the larger question of what freedom really means and to what extent it is in our possession at all. Several months later, Plath contemplated that question in her diary: “As for free will, there is such a narrow crack of it for man to move in, crushed as he is from birth by environment, heredity, time and event and local convention.”

For any sensitive and reasoning person, this bifurcation between the desire to be free and the awareness that we might not be is the source of immense and lifelong existential disquiet. “Freedom,” wrote the psychologist Rollo May “is the capacity to pause in the face of stimuli from many directions at once and, in this pause, to throw one’s weight toward this response rather than that one.” But are we really the ones who do the throwing, or is our weight moved between responses by the same impartial forces that propel the planets along their orbits? Is what we call choice really just the illusion of choice in a universe governed by immutable laws of physics and a large measure of randomness?

Neuroscientist Christof Koch offers a lucid yet palliative perspective in a portion of Consciousness: Confessions of a Romantic Reductionist (public library) — his fascinating inquiry into the central fact of our lives.

Koch begins with the commonest, most populist definition of free will, unevolved since the days of Descartes and the clockwork universe:

You are free if, under identical circumstances, you could have acted otherwise. Identical circumstances refer to not only the same external conditions but also the same brain states. This is the strong, libertarian, or Cartesian position, as it was articulated by Descartes, whom we keep encountering. Will with a capital “W,” the real thing.

But such a stringent definition, Koch notes, only lends itself to problems with binary, black-and-white answers — it begins to lose relevance and utility as the degree of complexity and nuance increases. Instead, he proffers a looser model of free will known as compatibilism, commonly endorsed by biologists, psychologists, physicians, and lawmakers:

You are free if you can follow your own desires and preferences. Determinism and free will can coexist. They are compatible with each other. Provided you are not in the throes of some inner compulsion, nor acting under the undue influence of other persons or powers, you are the master of your destiny. A long-term smoker who wants to quit but who lights up, again and again, is not free. His desire is thwarted by his addiction. Under this definition, few of us are completely free. Compatibilism does not appeal to otherworldly entities such as souls. It is all of this earth.

For an extreme example of compatibilism in action, Koch points to the Buddhist monk Thich Quang Duc, who famously set himself on fire in 1963 to protest the tyrannical regime in South Vietnam and burned to his own death with silent composure, not once flinching from his lotus position. Koch considers the universal truth within the fact of this particular action:

For the rest of us, who struggle to avoid going for dessert, freedom is always a question of degree rather than an absolute good that we do or do not possess.

Koch goes on to explore how the problem of free will changed as we moved from the clockwork universe of Newton’s day, wound out of any freedom by fixed physical laws that have pre-determined every future outcome since the beginning of time, to the conditional causalities of chaos theory and the ultimate death-blow to determinism in the uncertainty principle of quantum physics. Complement this particular fragment of Consciousness with neuroscientist Sam Harris on how acknowledging the illusoriness of free will liberates us and astrophysicist Janna Levin on living with moral responsibility in a universe bereft of free will.