At the end of a long day, I flop down on the couch and close my eyes. I burrow my face into a pillow and enjoy a few moments of silence. Yet one thought creeps into my consciousness. Go to the gym. Find your running shoes. It won’t kill you.

This is a familiar battle, one that I wage almost daily. When I do make it to the gym, I anoint myself a hero. What strength of character! Such self-control!

Is that really the case? Or are my thoughts and actions just a natural outcome of the laws of physics? In “Finding Free Will,” Christof Koch tackles this question with insights from physics, neurobiology and psychology. Although we do not yet have an answer, we can examine one of the vultures preying on our thoughts: our unconscious mind. Ingenious experiments allow us to observe the brain churning out impulses beneath our awareness, which our conscious mind then seeks to justify.

The question of free will is not merely cocktail-party banter. How we hold people responsible for their actions matters both to the legal system and to our day-to-day relationships. Those judgments become particularly challenging if mental illness is involved. For this reason and many others, the upcoming radical update to the premier resource for psychiatrists, the Diagnostic and Statistical Manual of Mental Disorders, better known as the DSM, has stirred up vigorous debate. Ferris Jabr investigates how the guidebook will add, redefine and eliminate certain disorders, reshaping the landscape of disease diagnoses in the process.

Even in a healthy state of mind, our notions are not necessarily freely chosen. The special report on religious belief, explores how genetics, upbringing and culture help to shape our attitudes toward divinity. Outside forces, it seems, intrude on just about every mental state.

Yet I can’t help but believe I am somewhat in control. At least when it comes to my mental and physical health, I know what to do. And that is to pry myself off the couch, lace up my running shoes and unleash the physical laws of the treadmill.