Neuroscientists and philosophers swim together in a pool of loaded words and phrases: “consciousness”, “free will”, “attention”, “decision making”, and so forth. Because defining these concepts is important to both fields, semantic debate tends to muddy the water. For instance, do we have free will?  Don’t worry…I’m not here to convince you that my view should pile on top of the seemingly infinite amount of literature covering this topic since the ancient Greeks began writing about it. Instead I will offer my brief opinion of what “free will” means, but only as an example to highlight the fundamental challenge at hand: words and short phrases are inadequate to capture the complex reality of nervous systems.

Words are inherently simple representations, and we generally need more words to explain more complex concepts. Consider the brain: one could spend their entire life reading articles and books about it and still not know everything. The world is complicated, and so are the nervous systems that must interact with it [1]. If we assume a Physicalist view, then we believe that mind and body are one [2]. It follows that thoughts and actions are somehow the products of the beaming electricity in our neurons, and thus the term “free will” makes a claim about how that happens. But if complexity requires more words, why would we restrict the way we think about the most complex system known (i.e. the nervous system, arguably) by boiling it into a single phrase?

My simple answer is that the concept of free will came well before our modern understanding of neurobiology. In fact, it essentially came before all modern branches of science as part of the natural philosophy of the ancient Greeks. However, the last couple of millennia have generated an astronomical amount of data about the nature of the universe and of life. From philosophy sprung physics, chemistry, biology, and psychology, and if you tie them all together you get neuroscience knocking on the door with claims of scientific proof that “free will is an illusion” [3], and a myriad of consequences to our societal foundations of justice and responsibility. The problem with making such a claim is this: nobody really knows what is meant, or worse – everyone assumes a different meaning and an infinite semantic debate ensues.

Example: an amateur’s minimal response to “do we have free will?”
(see [2] and [4] for a more thorough discussion, which is beyond to scope of this post)

When I see the term “free will”, I am usually reminded of one of my favorite scientific books:  QED: The Strange Theory of Light and Matter by physicist Richard Feynman [5]. In it Feynman elegantly explains that almost all known phenomena can be accounted for by quantum electrodynamics (QED, also a play on the latin phrase ‘quod erat demonstrandum’ that appears at the end of mathematical proofs), which is an inherently probabilistic theory. One possible approach to answer “do we have free will?” is to ask a deeper and more abstract question: is the world deterministic?  If we believe the physicists and regard nature as a matter of probabilities, then we must conclude that the world is not deterministic. From QED principles, it may be theoretically possible to explain only the probability of something as complex as behavior. However, even this is practically impossible. We can’t even completely describe the behavior of simple molecules, let alone organized collections of trillions of them such as you or me.

But let’s imagine for a moment that the equations can be written and solved. Every situation and moment of time is unique, and there are many independently operating and interacting probabilistic agents such as other organisms and molecules in the environment. How each output in us, each muscle fiber and gland secretion, is influenced by this constant stream of input and the consolidation of all that came before (i.e. memories), under the constraints of genetics, random fluctuations, and widespread redundancy (i.e. many pathways in the nervous system can produce the same output) is what I call “free will”. Again, let’s imagine that we can derive a model of synaptic input onto each muscle fiber and secretion of the body for a given input. Then we do this for every other body in the world as well as for physical forces that act upon them such as the weather, etc. Because we cannot capture the entire history of the universe, we must approximate in part. Then we must update our model dynamically, and the end result would be a detailed explanation of behavior and society and culture.

Could we comprehend this result? Certainly not, and consequently we must have a concept of free will.  We simply cannot simultaneously track all of the parameters that influence the human experience. The concept of free will is an acknowledgement of the incomprehensible parameter space in the model above, even if it is just “an illusion”. Additionally, to me the idea that it is theoretically possible but practically impossible to make a comprehensive model of behavior does not reduce us to machines or obliterate moral responsibility. Well, maybe it does imply that I am like a machine, but the notion that I could be defined as an automaton with 100 billion interacting parts (i.e. neurons) which can encode a lifetime of experiences is not derogatory to me – it’s beautiful. And perhaps the societal implications surrounding the debate about personal “responsibility” [2] are what really makes “free will” a loaded phrase. This is a hairy issue that includes sociological definitions of right and wrong in addition to solving the model above, which is beyond my scope here.  Regardless, I believe that even collections of genetic predispositions and memories should be held accountable for crimes, in order to shape future behavior (via others’ learning and memory) in our society.

The previous three paragraphs are my minimal description of “free will” (albeit long, and similar to the Libertarian perspective [2]). Hopefully it was coherent. If not, then maybe I needed to employ more words to explain my view, or choose my words more carefully. Is my definition what came to your mind when I first posed the question above, “do we have free will”?  Unlikely. There are simply many ways to interpret the question, and philosophers would immediately recognize that the question is not binary at all. Biologists may remind us that even bacteria could be considered to have a will [6]. Perhaps we could pose a more germane question to the Physicalist: “how do nervous systems work?”

So you’re telling me to write a book every time I use a word like “attention”?

The world is complicated, and so are the nervous systems that must interact with it. Words and phrases that attempt to condense this complexity too much inherently invite semantic debate. However, certain words or phrases may be unavoidable given their historical usage or, more practically, given word count and page limits in publications. The more complex the subject matter, the more difficult the speaker or writer’s job will be to boil everything down. There is some hope that the language of mathematics and computational modeling can help to form more compact representations of complexity (for example, see a recent valiant attempt in neuroscience in [7]). However, it is unclear if we will ever be able to extend that approach to meet the challenges of philosophy and psychology in generally defining “free will”, “consciousness”, “emotion” (see [8] for an excellent discussion of this word), “attention”, “decision making”, “sensorimotor transformation”, “action selection”, and so on. The inadequacy of words is very pervasive at many levels of neuroscience, and the job of neuroscientists (working with philosophers, psychologists, and other related fields) is to fight the battle against ambiguity constantly, to come up with more compact descriptions of the most exceedingly complex thing known to us. This is the ultimate challenge and joy of neuroscience – just don’t expect a complete answer from a short blog post.

Selected references:

1.   Kording K: Decision Theory: What “Should” the Nervous System Do? Science 2007, 318:606–610.

2.  Shadlen MN, Roskies AL: The Neurobiology of Decision-Making and Responsibility: Reconciling Mechanism and Mindedness. Front. Neurosci. 2012, 6(56).

3.  Smith K: Taking aim at free will. Nature 2011, 477:23–25.

4.  O’Connor T: The Stanford Encyclopedia of Philosophy. Fall 2010 Edition. Ed. Zalta, Edward. URL =

5.  Feynman R: QED: The Strange Theory of Light and Matter. Princeton University Press; 1985.

6.  Shapiro JA: Bacteria are small but not stupid: cognition, natural genetic engineering and socio-bacteriology. Stud. Hist. Philos. Biol. & Biomed. Sci. 2007, 38:807–819.

7.  Friston K: The free-energy principle: a unified brain theory? Nat. Rev. Neurosci. 2010, 11:127–138.

8.  LeDoux J: Rethinking the Emotional Brain. Neuron 2012, 73:653–676.