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The debate over whether human behaviour is the product of free choice or is instead fixed by forces beyond our control is one of the oldest and most fundamental in psychology, and it cuts to the heart of what kind of discipline psychology is. The tension is sharp: psychology wants to be a science, and science assumes that events have causes, yet much of how we treat each other — praising, blaming, holding people responsible — presupposes that people could have chosen otherwise. For Edexcel 9PS0 this issue is examined on Paper 3, where you must distinguish free will from determinism, break determinism down into hard and soft forms and into biological, environmental and psychic types, and weigh the scientific emphasis on causal explanation against the demands of moral and legal responsibility.
By the end of this lesson you should be able to define free will and determinism; distinguish hard from soft determinism and identify biological, environmental and psychic determinism with course examples; explain the scientific emphasis on causal explanation and the Libet challenge; and evaluate the debate's implications for moral and legal responsibility, reaching a reasoned position (usually soft determinism).
Key Definition: Free will is the idea that human beings are self-determining and able to choose their own thoughts, feelings and actions, free from the control of internal or external forces.
Key Definition: Determinism is the view that all behaviour has a cause, so that every event — including human thought and action — is the inevitable result of preceding causes and is, in principle, predictable.
Edexcel 9PS0 — Paper 3: Psychological Skills (Issues & Debates). This lesson develops the free will and determinism debate, which Edexcel expects you to apply across the specification rather than treat in isolation. You must be able to define free will, distinguish hard from soft determinism, and identify biological, environmental and psychic determinism, then evaluate the debate's consequences for responsibility, the legal system and therapy.
| Assessment Objective | What it looks like on this debate |
|---|---|
| AO1 — knowledge & understanding | Defining free will and determinism; distinguishing hard from soft; outlining the three types of determinism with course examples. |
| AO2 — application | Reading a study or scenario through the debate — e.g. classifying an explanation of aggression as biologically deterministic, or a phobia as environmentally deterministic. |
| AO3 — analysis & evaluation | Weighing determinism's fit with science against unfalsifiability; judging the responsibility implications; arguing why soft determinism is usually most defensible. |
Connects to…
A recurring examiner theme is that the most defensible position is usually soft determinism, and that this debate connects tightly to the psychology as a science and nature-nurture debates elsewhere in the course.
Determinism is best pictured as a continuum, from the claim that we have no freedom at all to positions that try to make freedom and causation compatible:
graph LR
H["Hard determinism<br/>Free will is an illusion;<br/>all behaviour is caused"] --- S["Soft determinism<br/>Behaviour is caused but<br/>not coerced; room for choice"] --- F["Free will<br/>People are genuinely<br/>self-determining"]
Key Definition: Hard determinism holds that all behaviour is caused by factors beyond our control, so free will is an illusion: given the prior causes, the behaviour could not have been otherwise.
Hard determinism comes in three flavours that map directly onto the approaches you have studied.
Biological determinism explains behaviour through genes, brain structure, neurochemistry, hormones and evolution. Twin studies imply a strong heritable component to traits such as intelligence and vulnerability to mental illness (for example, the higher concordance for schizophrenia in MZ than DZ twins reported by Gottesman and Shields, 1966); the dopamine hypothesis treats schizophrenic symptoms as the product of neurotransmitter dysfunction; and links between testosterone and aggression, or the role of the autonomic nervous system in the fight-or-flight response, are typically framed deterministically. On this view, the person is the downstream effect of their biology.
Key Definition: Environmental determinism holds that behaviour is shaped entirely by the environment — by conditioning, reinforcement and the conditions of learning.
Skinner (1971), in Beyond Freedom and Dignity, argued explicitly that free will is an illusion: behaviour is controlled by environmental contingencies of reinforcement, and the sense of choosing is itself a product of our conditioning history. The Learning Theories account of phobias (acquired through classical conditioning, as in the Little Albert demonstration) is a concrete course example of environmental determinism.
Key Definition: Psychic determinism holds that behaviour is caused by unconscious conflicts, drives and childhood experiences over which we have no conscious control.
Freud is the source here: adult behaviour is the inevitable outcome of interactions among the id, ego and superego, shaped by the psychosexual stages, and even apparently trivial "choices" such as slips of the tongue ("Freudian slips") betray unconscious causation. (Edexcel students meet the psychodynamic perspective as a classic contrasting explanation when comparing approaches.)
| Type of determinism | Approach | Cause of behaviour | Course example |
|---|---|---|---|
| Biological | Biological | Genes, neurochemistry, hormones | Dopamine hypothesis of schizophrenia; testosterone and aggression |
| Environmental | Learning Theories | Conditioning, reinforcement | Phobia acquired by classical conditioning (Little Albert) |
| Psychic | Psychodynamic | Unconscious conflict, childhood experience | Adult personality fixed in the psychosexual stages |
Behind all three lies scientific determinism: the assumption, built into the scientific method, that every event has a cause that can in principle be identified, so that the laboratory experiment seeks to establish that if X, then Y. This is why the debate is so consequential for psychology's identity. If behaviour were genuinely free and uncaused, it would be unpredictable and therefore beyond scientific explanation; so the more successfully psychology specifies the causes of behaviour, the smaller the apparent space for free will. The advance of neuroscience, in particular, has sharpened this pressure.
Key Definition: Soft determinism, or compatibilism, is the view that all behaviour has a cause, yet people are still meaningfully free to the extent that their behaviour is not coerced or constrained by external force. Behaviour can be both determined and, in this qualified sense, freely chosen.
William James was an early advocate: he distinguished caused behaviour from coerced behaviour and argued that we are free when we act on our own reasons and desires, even though those reasons themselves have causes. The cognitive approach is broadly soft-deterministic — it accepts that behaviour is shaped by prior causes (schemas, biases, prior learning) while insisting that people actively process information, interpret situations and select responses rather than being passively pushed by stimuli.
Bandura's reciprocal determinism captures the position vividly: behaviour, personal/cognitive factors and the environment all influence one another bidirectionally, so the individual is shaped by their environment but also acts back on it, exercising personal agency within a causal web.
graph LR
B["Behaviour"] --> E["Environment"]
E --> B
B --> P["Personal / cognitive factors"]
P --> B
E --> P
P --> E
Exam Tip: Soft determinism is usually the strongest evaluative position because it dissolves the apparent contradiction between science and responsibility. If asked to conclude, explain why the distinction between caused and coerced lets us keep causal explanation and meaningful choice at the same time.
The clearest commitment to free will on the course is the humanistic approach. Rogers (1951) held that people have an innate drive towards self-actualisation, and his person-centred therapy is built on the premise that the client, not the therapist, directs change — the therapeutic conditions free the client to make their own meaningful choices. Maslow (1943) likewise implies free will: once lower needs are met, the person is free to pursue growth and self-actualisation. The humanistic position is that people are active agents who choose their behaviour and take responsibility for it, and that reducing them to biology or conditioning misses what is distinctively human.
Three further considerations are usually offered in support of free will. First, subjective experience: the everyday, vivid sense that we deliberate and choose is hard to dismiss as pure illusion. Second, the legal and moral order: holding people responsible — praising, blaming, punishing — only makes sense if they could have acted otherwise. Third, the practical effects of belief: Vohs and Schooler (2008) found that participants led to believe free will does not exist subsequently cheated more, suggesting that belief in free will supports prosocial behaviour and personal responsibility — so even if free will cannot be proven metaphysically, the concept does real moral work.
The most-cited empirical challenge to free will comes from Libet et al. (1983). Participants were asked to flex a wrist whenever they felt the urge, while watching a fast-moving clock so they could report the exact moment they became consciously aware of the decision. The researchers recorded three things: the readiness potential (a build-up of electrical activity in the motor cortex), the participant's reported moment of conscious intention, and the movement itself.
The striking result was that the readiness potential preceded the participant's reported awareness of deciding by a few hundred milliseconds: the brain appeared to initiate the action before the person was consciously aware of choosing it. On the face of it, this suggests that conscious will does not cause our actions but arrives after the brain has already begun them.
Libet's own interpretation was more careful, and you should reproduce it precisely. He argued that although the initiation of action is unconscious, participants could still consciously veto the movement in the brief window after becoming aware of the urge — a capacity he called "free won't" rather than free will. So the study constrains, rather than abolishes, the role of consciousness.
Exam Tip: Be exact about Libet et al. (1983): the readiness potential preceded conscious awareness of the decision, not the action alone, and Libet himself argued for a conscious veto ("free won't"). Misremembering this is a common way to lose credibility in an essay.
The debate is not merely abstract; its consequences are exactly where the AO3 marks concentrate.
| Position | Implication for moral responsibility | Illustration |
|---|---|---|
| Hard determinism | No one is ultimately responsible — behaviour is caused | A defendant whose violence is attributed to a brain tumour |
| Soft determinism | Responsible for actions that are not coerced | A person who chooses to steal is responsible; one forced at gunpoint is not |
| Free will | Full responsibility — people always choose | Every act is praiseworthy or blameworthy |
The legal system broadly assumes free will (and therefore responsibility) but builds in deterministic exceptions: diminished responsibility acknowledges that mental disorder can impair choice, and automatism treats genuinely involuntary acts (for example during a recognised sleep disorder) as not freely chosen. This frames a live policy question — should justice emphasise punishment (assuming free choice) or rehabilitation (assuming addressable causes)?
In therapy, the positions cash out as different treatment philosophies: behavioural therapies such as systematic desensitisation are deterministic (maladaptive behaviour is learned and can be unlearned); biological treatments such as drug therapy are deterministic (disorder has a correctable biological cause); humanistic person-centred therapy assumes free will (the client has the power to grow); and CBT is neatly soft-deterministic — it treats negative automatic thoughts as learned yet trains the client to choose to challenge them. Because Edexcel's Clinical Psychology application requires you to evaluate treatments, this therapy-level reading of the debate is directly examinable.
Determinism is consistent with the aims and successes of science, which is the strongest argument in its favour. The experimental method presupposes that behaviour has identifiable causes, and adopting that assumption has been highly productive: deterministic explanations have generated effective interventions, from antipsychotic drugs (biological determinism) to systematic desensitisation (environmental determinism). The implication is that determinism is not just a philosophical preference but a working assumption that pays off in prediction, control and treatment, which is hard to reconcile with a strong free-will view. If behaviour were genuinely uncaused, these systematic, replicable treatment effects would be inexplicable.
However, hard determinism may be unfalsifiable, which weakens its scientific credentials. Because any behaviour can be explained after the fact as the inevitable product of some prior cause, the claim that everything is determined can be made immune to disconfirmation — there is no observation that would count against it. This matters because falsifiability is a hallmark of good science (a point developed in the psychology as a science lesson), so the irony is that an over-strong determinism becomes as unscientific as the free will it dismisses. The implication is that determinism is most defensible as a methodological assumption (we look for causes) rather than as a proven metaphysical truth.
Hard determinism has troubling consequences for moral and legal responsibility, which is a serious practical objection. If no one could ever have acted otherwise, then concepts of blame, desert and punishment lose their footing, and the criminal-justice system rests on a fiction. The legal system implicitly recognises the tension by allowing deterministic defences (diminished responsibility, automatism) only as exceptions to a default of responsibility. The implication is that a workable account of human conduct must preserve some notion of responsibility, which is exactly what soft determinism is designed to do — and this is a major reason the soft-deterministic position is so widely adopted.
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