The law of parsimony, a problem-solving principle, states that the simplest explanation for something is typically the most likely. The term ‘parsimony’ comes from the Latin parsimōnia, which is rooted in the idea of acting (‘act’) sparingly or refraining from excess, emphasizing the importance of economy and restraint in explanations.
When discussed in the context of psychology, parsimony refers to seeking explanations and theories that are practical, with clear conclusions, to address mental health issues. The approach can be very helpful, as often, people who seek out psychological help find the unnecessary complexity in breaking down their underlying issues overwhelming. For clinicians and researchers, parsimony can be used to narrow down the most likely causes and factors among the variables they are trying to understand. In this process, each ‘character’—such as a specific trait or feature of a patient’s behavior or symptoms—can be considered to determine which are most informative for analysis.
Parsimony is valuable for clinicians and researchers because it guides the decision process in selecting the most likely explanation, helping them focus on the most relevant information and avoid overcomplicating their assessments.
Defining the Parsimony Principle
The term “parsimony” was derived from the Latin word parser, meaning to be sparing. The general meaning of the word is excessive thriftiness or frugality. In some contexts, this has a negative connotation, suggesting a lack of generosity or miserliness. However, there is also value in the concept of parsimony. Parsimony in psychology entails identifying the simplest and most accurate explanation for brain processes and human behaviors.
The law of parsimony suggests identifying the simplest, least complicated explanation of a situation or observation. Explanations are often structured in a particular form, and the simplest form is generally preferred according to this principle. Even philosopher Aristotle supported this method, saying, “The more limited, if accurate, is always preferable.” Scientific laws and explanations should be interpreted in their simplest form, aligning with the principle of parsimony.
The law of parsimony is often referred to as Occam’s razor. It was named after theologian William of Ockham in the 1300s, who authored the term “numquam ponenda est pluralitas sine necessitate.” This means “Plurality must never be posited without necessity.”
Years later, scientist Sir William Hamilton named the phrase “Occam’s razor” to describe the process of “shaving away” unnecessary or peripheral assumptions in logical reasoning. Subsequently, scientists in varying fields adopted this practice in their studies. It involves using the fewest steps, with minimal resources, leading to the optimal conclusion (Simms, n.d.).
Applications of Parsimony in Research
The parsimony principle is more than just a theoretical guideline—it’s a practical problem-solving principle that shapes the way researchers approach complex questions across psychology, science, and philosophy. When faced with a data set full of variables and potential explanations, researchers rely on parsimony to guide their search for the simplest explanation that still makes sense given the evidence.
In research, applying the parsimony principle means carefully evaluating which factors are truly necessary to explain a phenomenon. For example, suppose a psychologist is studying the relationship between stress and sleep quality. There may be dozens of possible variables—diet, exercise, genetics, environment—but the parsimony principle encourages the researcher to focus on the most direct and impactful factors first. By doing so, they can determine which hypotheses are supported by the data without introducing unnecessary complexity.
This approach is especially valuable when comparing different models or theories. Researchers often develop multiple hypotheses to explain a set of observations, but the most parsimonious model—the one that requires the fewest assumptions and variables—is typically preferred. This doesn’t mean ignoring important data, but rather ensuring that every factor included in the explanation is justified by necessity, not just by possibility. In other words, the simplest explanation that fits the evidence is usually the best starting point.
The value of parsimony extends beyond psychology. In fields like law and public policy, the principle is used to analyze the necessity and proportionality of different actions or punishments. For instance, when developing justice policies, lawmakers may use the parsimony principle to argue for solutions that are effective without being overly severe or complex, promoting fairness and clarity.
By using parsimony as a framework, researchers and policymakers can save time, reduce confusion, and improve the quality of their decisions. The principle helps to clarify the relationship between variables, streamline the process of hypothesis testing, and ensure that explanations are both understandable and evidence-based.
Ultimately, the parsimony principle is a powerful tool for anyone seeking to make sense of complex data or phenomena. It encourages a disciplined approach to problem-solving, where simplicity, clarity, and necessity guide the search for understanding. Whether analyzing a psychological study, developing a new theory, or crafting public policy, the principle of parsimony helps ensure that our explanations are as straightforward and effective as possible—without sacrificing accuracy or depth.
Benefits of Applying the Simplest Explanation in Psychology
Brain function is complex, and much of it remains a mystery. While scientists are committed to simplifying the study of psychology and human behavior, there is still a gap in understanding. Parsimony can make psychology less abstract and more tangible. A good therapist or mental health professional can use this framework to provide accurate and valid explanations that are relatable and easy to understand. Parsimony also provides a measure for evaluating the quality of explanations, helping to determine which ones are most effective and grounded in evidence.
Parsimony ensures that explanations are simple and helpful and do not rely on unsupported assumptions. It also relies on tangible observations and proven data with replicable results. Parsimonious descriptions may include physical objectives, activities, facial expressions, or test results.
Parsimony is not about taking the fastest route. Rather, it’s about finding the most efficient, comprehensive, and effective path possible. If there is a simpler yet equally thorough solution, this is the desired choice. Parsimony leads to a reduction in unnecessary complexity, ensuring that solutions remain both effective and manageable. This simplicity also makes communication easier, therefore increasing the chances that concepts are understood. Parsimony helps to store information more concisely and understandably, making it easier to recall and share.
In the spirit of parsimony, let’s break it down. Parsimony is all about:
- Using the fewest assumptions.
- Choosing the simplest explanation that fits the evidence.
What the Critics Say
Sounds simple enough, right? It may sound straightforward, but it requires discipline to apply effectively. Unfortunately, it’s easy for psychologists to overcomplicate things. Critics worry that there is a broad gray area in psychology, and this can make it difficult to explain complicated behaviors and cognitive processes. For parsimony to be effective, certain logical and methodological constraints must be satisfied. It is also important to respect the balance between simplicity and complexity when applying parsimony, ensuring that essential details are not lost in the pursuit of simpler explanations.
Final Thoughts
Finally, in trying to understand a problem, experts can often have a bias toward the more interesting, complicated, or familiar explanations. While they may be correct, it’s wise to begin by considering the simplest possible solution and testing that first. If the most obvious answers prove to be incorrect, it then makes sense for the explanations to increase in complexity as the straightforward ones are dismissed.
The principle of parsimony is rooted in scientific and philosophical traditions, emphasizing the value of simplicity and efficiency in problem-solving and theory development.
Sources
- APA Dictionary of Psychology. (n.d.). https://dictionary.apa.org/law-of-parsimony
- Battig, W. F. (1962). Parsimony in Psychology. Psychological Reports, 11(2), 555–572. https://doi.org/10.2466/pr0.1962.11.2.555
- Epstein, R. (19840). The principle of parsimony and some applications in psychology. Journal of Mind and Behavior, 5(2), 119–130. https://www.jstor.org/stable/43853318
- Simms, C. (n.d.). Occam’s razor. New Scientist. Retrieved July 27, 2025, from https://www.newscientist.com/definition/occams-razor/
Karen Doll has been a Licensed Psychologist in the Twin Cities for 20 years, working in organizational consulting. She leverages her education in Clinical Psychology with her leadership assessment expertise in her practice. She is an executive coach focusing on helping people maximize their potential.