Source: Chapter 3, Section 3.1 lecture slides
Difficulty: Introductory | Prerequisites: None, though familiarity with basic logic (valid arguments, premises, conclusions) is helpful.
This section sits at the heart of any introductory philosophy course: the question of whether human beings can act freely or whether every action is the inevitable product of prior causes. It matters because free will underpins moral responsibility, legal accountability, and everyday judgements about praise and blame. You do not need any background in physics or psychology to follow the arguments, but you should be comfortable reading a short formal argument (premises leading to a conclusion). The section introduces several rival positions, from hard determinism to indeterminism, and shows why each runs into trouble.
Causal determinism says every event has a cause, which seems to rule out free will. Hard determinists accept that conclusion; indeterminists reject it by saying some events are uncaused, but that brings its own problem, because a random event is not a free choice either. Neither extreme on its own rescues the kind of freedom most people think they have.
Causal determinism
The doctrine that every event has a cause that makes it happen. Given the prior state of the universe and the laws of nature, only one outcome is possible.
In simple terms, this means: everything that happens was guaranteed to happen by whatever came before it.
Hard determinism
The doctrine that there are no free actions. It accepts causal determinism and adds that causal determinism is incompatible with free will, so free will does not exist.
Think of it as: the universe is a chain of dominoes, and your choices are just dominoes falling like the rest.
Incompatibilism
The view that causal determinism and free will cannot both be true. Hard determinists are incompatibilists who side with determinism. (Some incompatibilists side with free will instead; they are called libertarians in the philosophical sense.)
In simple terms, this means: you have to pick one, determinism or free will. They cannot coexist.
The Consequence Argument
A formal argument for incompatibilism. If determinism is true, every event follows from past events plus the laws of nature; we cannot change the past or the laws; therefore we cannot change our actions; therefore we cannot act freely.
Think of it as: if the script was written before you were born and you cannot rewrite it, you are not improvising.
Causal indeterminism
The view that some events are not the consequence of past events plus the laws of nature. Under this view, the future is not fixed.
In simple terms, this means: the universe leaves some things genuinely open. Not everything is locked in.
Indeterminism (about free will)
The doctrine that free actions are uncaused. At any point in history, there are many possible futures.
Think of it as: your choices are like forks in a road that truly branch, rather than a single rail.
Nature/nurture debate
The question of which factor, genetics or upbringing, has a greater effect on our behaviour.
In simple terms, this means: are you shaped more by your DNA or by how you were raised?
Quantum indeterminism
The finding from physics that some events at the sub-atomic level have no cause, which means the doctrine of universal causal determinism is false.
Think of it as: even nature does not always follow a strict script at the smallest scales.
Causal determinism holds that every event has a prior cause that necessitates it.
The central tension: if every human action is caused by earlier events, then no one could have done otherwise, and freedom seems impossible.
This is the starting point for the entire debate in this chapter.
Hard determinism accepts two claims:
(1) Causal determinism is true.
(2) If causal determinism is true, there are no free actions.
Conclusion: there are no free actions.
Hard determinists are a subset of incompatibilists, those who believe determinism and free will cannot coexist.
The most influential formal argument for incompatibilism:
(1) If causal determinism is true, every event is the consequence of past events plus the laws of nature.
(2) We are powerless to change past events, laws of nature, or their consequences (which include our actions).
(3) If we are powerless to change our actions, if we cannot do otherwise, then we cannot act freely.
(4) Therefore, if causal determinism is true, we cannot act freely.
The argument's force comes from premise (2): the past is fixed and the laws are fixed, so anything that follows from them is fixed too.
Hard determinists extend the argument to moral responsibility:
(1) If causal determinism is true, we cannot act freely.
(2) If we cannot act freely, we cannot be held responsible for our actions.
(3) Therefore, if causal determinism is true, we cannot be held responsible for our actions.
This has large consequences for ethics, law, and everyday judgements of praise and blame.
Some thinkers argue that science confirms hard determinism. B.F. Skinner claimed that "personal exemption from a complete determinism is revoked as a scientific analysis progresses."
The nature/nurture debate sits inside this conversation:
Those who favour nature say genes are the primary determinant of behaviour.
Those who favour nurture say upbringing and environment are the primary determinant.
Both sides assume behaviour is determined; they disagree only about which causes matter most.
Physics undercuts universal causal determinism: at the sub-atomic level, some events appear to have no cause at all.
Quantum mechanics gives us an extraordinarily successful understanding of the physical world, and it admits uncaused events.
This means the claim that science supports determinism is oversimplified. The best-confirmed physical theory we have is, in fact, indeterministic.
Causal indeterminism is the view that some events are not the consequence of past events plus the laws of nature.
Under this view, the future is not fixed; more than one outcome is genuinely possible at any moment.
This opens logical space for free will, but does not by itself deliver it (see the next section on why).
Indeterminism (about free will) says free actions are uncaused. At any point in history, many futures are possible.
The trouble: if an action is uncaused, it is random, and a random event does not look like a free choice.
Taylor's Unpredictable Arm illustrates this. If Taylor's arm movements are undetermined, and his arm strikes someone, he is not responsible because he did not cause or intend the movement.
Uncaused actions cannot be considered free actions because where there is no intention, there is no genuine action.
For something to count as an action (rather than a mere event), it must be caused by the agent's intention.
Moral responsibility requires that you caused the action or failed to prevent it.
This creates the core dilemma of Section 3.1: determinism seems to rule out freedom, but indeterminism (randomness) does not deliver it either.
Laplace's Superbeing: Imagine an intelligence that knows every force in nature and the position of every particle. For this being, the future and the past would be equally transparent. If such prediction is possible even in principle, how can free will exist?
Gardner's Random Bombardier: A hydrogen bomb is dropped by a mechanism triggered by the click of a Geiger counter (a quantum event). Here, a micro-level indeterminate event produces a macro-level consequence. Indeterminacy is not safely confined to the sub-atomic world.
Taylor's Unpredictable Arm: Taylor's arm moves randomly, without his control. If it strikes someone, he bears no responsibility because he did not intend or cause the movement. This shows that indeterminism (randomness) does not give us freedom either.
Freedom and Foreknowledge (Thought Probe): If God is all-knowing and knows the future, can there be free will? Divine foreknowledge raises a parallel worry to causal determinism: a fixed future seems incompatible with genuine choice.
Genetic Cleansing (Thought Probe): If sociobiologists discover the genes that influence our psychology and we can alter them through genetic engineering, should we? This raises questions about how much of our behaviour is determined by biology and whether intervening changes the nature of responsibility.
The free will debate is not just abstract philosophy. Criminal law assumes people can choose their actions; if hard determinism is correct, punishment for wrongdoing loses its justification. Similarly, behavioural psychology (Skinner's operant conditioning) treats behaviour as fully determined by reinforcement history, which has shaped everything from classroom management to addiction treatment. The nature/nurture question feeds directly into debates about education policy, criminal sentencing, and genetic screening.
Students often think "determinism" and "fatalism" are the same thing. They are not. Determinism says events are caused by prior events; fatalism says outcomes are fixed regardless of what you do. A determinist can still say your actions matter (they are part of the causal chain).
Students often assume quantum indeterminism solves the free will problem. It does not. Randomness at the sub-atomic level does not give you control over your actions; it just means some events are uncaused.
Students often conflate incompatibilism with hard determinism. Incompatibilism is the broader claim that determinism and free will cannot coexist. Hard determinism is just one version, the one that sides with determinism. A libertarian (in the philosophical sense) is also an incompatibilist but sides with free will.
Students sometimes think the nature/nurture debate is separate from the determinism debate. Both sides of nature/nurture assume your behaviour is determined; they only disagree about the type of cause (genes vs. environment).
Be able to state the Consequence Argument in full (all four steps). This is a standard exam question.
Know the difference between causal determinism (a claim about the world) and hard determinism (a claim about free will that builds on causal determinism).
Be ready to explain why quantum indeterminism does not, by itself, rescue free will. Exams often test whether you understand the "both horns" problem: determinism threatens freedom, but so does randomness.
The link between free will and moral responsibility is commonly tested. Be prepared to reconstruct the three-step argument from determinism to "we cannot be held responsible."
Thought experiments (Laplace's Superbeing, Gardner's Random Bombardier, Taylor's Unpredictable Arm) are frequently used as short-answer or essay prompts. Know what each one illustrates and which position it supports or challenges.
True or false: Hard determinism says free will and determinism are compatible. ______
True or false: Quantum mechanics supports universal causal determinism. ______
Fill in the blank: The ______ Argument says that if determinism is true, we cannot change the past, the laws, or their consequences, so we cannot act freely.
True or false: According to indeterminism, uncaused actions count as free actions. ______
Fill in the blank: Incompatibilism is the view that causal determinism and ______ cannot both be true.
Answers: 1. False (hard determinism says they are incompatible). 2. False (quantum mechanics admits uncaused events). 3. Consequence. 4. False (uncaused actions are random, not free). 5. Free will.
Q: State the Consequence Argument. What conclusion does it reach, and what is its key premise?
A: (1) If causal determinism is true, every event is the consequence of past events plus the laws of nature. (2) We are powerless to change past events, laws of nature, or their consequences. (3) If we cannot change our actions, we cannot act freely. (4) Therefore, if causal determinism is true, we cannot act freely. The key premise is (2): the fixity of the past and the laws.
Q: Explain why quantum indeterminism does not automatically support free will.
A: Quantum indeterminism shows that some events at the sub-atomic level are uncaused, which refutes universal causal determinism. However, an uncaused event is random, and random events are not under the agent's control. Taylor's Unpredictable Arm illustrates this: if your arm moves randomly and hits someone, you are not responsible because you did not intend or cause the movement. Randomness is not freedom.
Q: What is the difference between incompatibilism and hard determinism?
A: Incompatibilism is the view that causal determinism and free will cannot both be true. Hard determinism is a specific form of incompatibilism that accepts causal determinism and concludes that free will does not exist. (A philosophical libertarian is also an incompatibilist but rejects determinism and affirms free will.)
Q: How does Gardner's Random Bombardier thought experiment challenge the idea that quantum indeterminacy only affects the micro-level?
A: In the thought experiment, a hydrogen bomb is triggered by the click of a Geiger counter, which is a quantum (micro-level) event. The resulting explosion is a macro-level event with enormous consequences. This shows that indeterminacy at the sub-atomic level can amplify into significant effects in the everyday world.
Q: If hard determinism is true, what follows for moral responsibility, and why?
A: If hard determinism is true, we cannot act freely (because our actions are the inevitable consequences of prior causes). If we cannot act freely, we cannot be held morally responsible for our actions, because moral responsibility presupposes that the agent could have done otherwise.
This material connects directly to compatibilism (likely covered in Section 3.2 or later), which tries to reconcile determinism with free will by redefining what "freedom" means. If you found both horns of the dilemma unsatisfying (determinism kills freedom, indeterminism gives you randomness instead), compatibilism is the attempt to find a middle path.
The moral responsibility argument connects to ethics more broadly: Kantian ethics assumes rational agents who can choose; utilitarian consequentialism cares about outcomes regardless of whether the agent "chose" freely. How you land on the free will question shapes which ethical framework makes sense to you.
The nature/nurture thread connects to philosophy of mind and philosophy of biology. If you take a course covering personal identity or consciousness, the question of what determines your behaviour will come back in a different form.
Free will, determinism, causal determinism, hard determinism, soft determinism, compatibilism, incompatibilism, libertarianism (philosophy), indeterminism, causal indeterminism, quantum indeterminism, Heisenberg uncertainty principle, Laplace's demon, consequence argument, moral responsibility, nature vs. nurture, B.F. Skinner, behaviourism, fatalism, agency, intention, uncaused events, could have done otherwise, principle of alternate possibilities, Taylor's unpredictable arm, Gardner's random bombardier, foreknowledge and free will, genetic determinism