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Reductionism refers to an approach that breaks complex phenomena into more simple components. It also implies that this process is desirable because complex phenomena are best understood in terms of a simpler level of explanation. Psychologists are drawn to reductionist explanation and methods of research as it is a powerful tool that has led to major discoveries. There are three levels of reductionism the first being the highest level. The highest level is associated with cultural and social explanations of how social groups affect our behaviour. The middle level is psychological explanations of behaviour and the lowest biological explanations of behaviour regarding how hormones and genes affect our behaviour. We can consider any behaviour in terms of all three levels. 

As well as there being levels of reductionism there are also different types of reductionism. Biological reductionism refers to refers to the way that biological psychologists try to reduce behaviour to a physical level and explain it in terms of neurons, neurotransmitters, hormones, brain structure. Since all animals are made up of atoms then human behaviour must be explainable at this level. Environmental reductionism is also known as stimulus-response reductionism. Behaviourists assume that all behaviour can be reduced to the simple building blocks of S-R (stimulus-response) associations and that complex behaviours are a series of S-R chains. Experimental reductionism reduces complex behaviours to isolated variables. 

Holism however is the opposite of reductionism as it perceives the whole experience rather than the individual features and/or the relations between them. Holism suggests that we can’t predict how the whole system will behave just from a knowledge of the individual components. Humanistic psychologists believe that the individual reacts as an organised whole, rather than a set of stimulus response (SR) links. 

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One benefit of biological reductionism is the real world application having aided the development of effective drug treatments including SSRIs that helps treat depression by increasing the level of the hormone serotonin. The development of drug therapies based on scientific evidence has led to a considerable reduction in institutionalisation and is a more humane approach as it doesn’t blame the patient. However, drug therapies aren’t wholly positive as their success rates are variable and treat the symptom instead of the cause meaning the effects might not be long lasting. Reducing mental illness to the biological level ignores the context and function of such behaviour. 

Environmental reductionism is associated with the behaviourist approach which was developed as a result of experiments involving non-human animals. Whilst these experiments are considered scientific due to their controlled environments taking places in labs which can lead to higher replicability it is argued that using animals is not reflective of complex human behaviour. Humans are not scaled-up versions of animals as our behaviour is influenced by social context and intention. This means even in animal studies reductionist explanations ignore other possible influences eg Cognition. 

Experimental reductionism allows us to establish cause and effect and helps to establish psychology as a science as it reduces behaviour to a form that can be studied, operationalising the variables. However, findings from lab experiments can’t be generalised to real-life as lab experiment results are often not replicated in real-life settings. For example, this can be seen with contradictory research into the effects of anxiety on eyewitness testimony. Whilst Johnson and Scott, using a controlled lab experiment, concluded anxiety has a negative effect of eyewitness testimony Christianson et al came to a different conclusion when studying victims of real-life bank robberies in Sweden. This means the operationalisation of variables may result in something that is measurable but bears no resemblance to the real thing meaning experimental reductionism is counterproductive. 

Whilst holistic explanations attempt to provide a complete and realistic understanding of human behaviour they do not establish causation seeing as they dont examine behaviour in terms of operationalised variables. By not using variables that can be manipulated and measured  holistic explanations are viewed as unscientific.