An Introduction to the
Logic of Scientific Method

by Craig Rusbult, Ph.D.

This page is a beginning.  It will help you understand the simplicity of scientific method in the simple "reality check" that is the main focus of scientific logic.  But along the way you'll also see other aspects of scientific thinking skills, and at the end you'll be invited to continue your exploration of "how it all fits together in a big picture" so you can understand the complexity of scientific methods and their potential applications in science education.

Part 1: The Foundation of Scientific Method — Logical Reality Checks      Experiments allow Observations & Theories allow Predictions Theory Evaluation (by comparing Observations & Predictions)      A Visual Summary of Scientific Method using Reality Checks Theory Generation (by an imaginative use of Reality Checks) Experiments — Creative Generation and Critical Evaluation	Parts 2 and 3: Scientific Method as Design Comparing Science and Design Does a scientific method exist? Controversy and Complexity A Model for Scientific Method

 
 

      The Foundation of Scientific Method — Logical Reality Checks

      You can understand and enjoy the adventure of science, because the thinking used in science is not strange and mysterious, it's the same thinking you use in daily life.  In scientific logic, as in daily life, you use reality checks to decide whether "the way you think the world is" matches "the way the world really is."  We'll begin by looking at three ideas and their interactive relationships during the central activity of modern scientific method, when observations and predictions are compared in a reality-check that is a test of quality for a theory:
 

      EXPERIMENTS allow OBSERVATIONS

      In science, information about nature comes from experiments that allow observations.  Consider two types of experimental situations:
      a) For several months you make observations about the moon's appearance, and the times and locations of its rising and setting.
      b) You observe the growth of young plants in many contexts, by varying many factors: light, temperature, type of seed (lima bean,...), type of soil, amount and frequency of watering, amount and type of fertilizer, treatment of seed (by soaking, cooking,...) before planting, and more.  You try different combinations of factors, and for each experiment you make observations both above and below the soil surface, before and after the plant grows through the surface.
      A) In an uncontrolled experiment (like observing the moon) the situation is set up by nature.  B) In a controlled experiment (with seeds) humans set up the situation, but "what happens" depends on nature.  The degree of human control, in setting up an experimental situation, can range from no control through partial control to total control.
      We observe using human senses (to see, hear, touch, taste, or smell) plus instruments (watch, ruler, scale, pipet, compass, thermometer, microscope, telescope, spectrometer, chromatograph,...) that help us measure more precisely and observe more widely.
      We translate raw data (from senses or instruments) into "observations" that we record using symbolic representations that are verbal (words,...), visual (pictures,...), and mathematical (numbers,...).
 

      THEORIES allow PREDICTIONS

      A theory is a human attempt to describe and/or explain our observations of what happens, or (in historical science) what has happened.  A descriptive theory claims only to describe what happens.  An explanatory theory claims to describe what happens and also why it happens.
      With a descriptive theory, predictions are made by generalizing, by assuming that "what happened before will happen again."  Or, using if-then logic: "If this situation is similar to previous situations (as claimed by the theory), then we should expect a result that is similar."  For example, you could predict the time and location of the moonrise on Wednesday, based on patterns you recognized while thinking about observations from Sunday, Monday, and Tuesday.
      An explanatory theory claims to explain "how and why things are happening" in an experimental system by describing — verbally, visually, and/or mathematically — the system's composition (what it is) and operation (what it does).  You can use this model to make predictions by answering the question, "In this situation, if the composition-and-operation model is true (as claimed by the theory), then what will happen and what will we observe?"
      With either type of theory, the if-then inference is similar.  You think, "In this situation, IF the system behaves as expected (according to the theory), THEN we will observe ___" and what you put in the blank is your theory-based prediction.
      When scientists make an if-then inference, they can move from IF to THEN in a variety of ways.  They might remember what has happened in the past, and estimate how similarities and differences in situations (when comparing previous situations with the current situation) will translate into similarities and differences in observations.  Or, if a theory includes an equation or a model, they could substitute numbers into the equation and calculate, or "run the model" in their minds or in a physical simulation or computer simulation.  If predictions can be made using several methods, this will serve as a check on the predicting methods and a cross-check on the predictions.
      A theory-based inference about "what will happen and what will be observed" can be made either before or after observations are known.  When an inference is made after observations are known, there is more concern about unconscious bias or conscious cheating, since non-valid logic could be used in an attempt to achieve a match between the inference and the known observations.  But inferences with either timing are logically equivalent if each is obtained using valid logic, and in science both are called "predictions".

 
      • THEORY Evaluation
      The logical foundation of scientific method is the reality check.  By observing reality and using logic, scientists can decide whether a theory about "the way it is" corresponds with "the way it really is."
      A physical experiment allows observations of what nature actually does, and a mental experiment lets us make predictions about what nature will do.  In a reality check, scientists compare OBSERVATIONS with THEORY-based PREDICTIONS.  If a theory fails in reality checks because its predictions do not match observations, scientists can reject the theory.*  By contrast, a correct prediction does not prove a theory is true, because other theories (current or future) might make the same correct prediction.  To distinguish between two theories, we need to observe what happens in a situation where the two theories make different predictions.  {* But a decision to reject a theory is a judgment call, and scientists may be cautious about immediately claiming "falsification" after a failed reality check, due to the possibility that their knowledge (of the situation, observations, or predictions) is inaccurate. }
      Multiple Independent Confirmations:  When a theory makes correct predictions in a wide variety of independent areas, and alternative theories make incorrect predictions, this provides strong evidence that the repeatedly confirmed theory is true.
      Usually, empirical factors (based on reality checks) are the main factors in theory evaluation.  But scientists also consider conceptual factors such as a theory's logical characteristics (like internal consistency and structural simplicity) and its relationships with other currently accepted theories.  Scientists are also influenced by cultural-personal factors (such as personal desires, group pressures, philosophical or religious views, and cultural thinking habits) but most scientists think the quality of science decreases when these factors affect the results of theory evaluation.
      The overall result of theory evaluation is an estimate of theory status.  This status, which can range from very low to very high, indicates the scientists' confidence in a theory.  Most scholars who study science think we cannot logically prove a theory is either true or false, but we can develop a rationally justified confidence in our conclusions.

 
      A VISUAL SUMMARY
      The diagram below, which shows the essence of scientific method, has three main elements: OBSERVATIONS & PREDICTIONS (these two are compared in a REALITY CHECK) and THEORY.  If you study the diagram and think about what you've been reading, it should make sense.  Notice the arrows pointing away from THEORY (because a theory is used for making the predictions used to evaluate a theory, as explained above) and toward THEORY (because observations are used to generate a theory, as explained below).

   

 
      • THEORY Generation
      The focus now shifts from evaluation to generation, with thinking that is both creative and critical, when we ask "Where do scientific theories come from?"
      Usually, scientists work with theories that already exist.  But earlier in the history of science these theories had to be generated.  And sometimes current scientists invent their own new theories, usually by revising old theories.  Typically, the process of generation is different for a descriptive theory and explanatory theory.
      A descriptive theory is generated when scientists recognize a pattern, when they notice that in a certain type of situation a particular result happens.  They describe the observed regularity by claiming that "In this situation (when ___ ), ___ will happen."  For example, we can say that "When an object is released, it will fall toward the ground."  But is this theory always correct?  How do we react, thinking as scientists, when we see that some objects — such as a helium balloon, bottle rocket, or bird — do not fall?  We revise our general theory, limiting its claims by saying that "In most situations, a released object will fall downward."  And we try to find theories that explain why the regularity occurs, and why the exceptions occur.  For example, we can explain the rising of a helium balloon by proposing the existence of an upward buoyant force that causes lighter-than-air objects to rise in air.  And we can generalize this force to other objects and fluids, to also explain why a cork floats on water.
      An explanatory theory is usually generated by a process of creative thinking in which imagination is guided by the logic of reality checks, with creativity being stimulated by observations and guided by critical thinking.  In prediction we ask a cause-to-effect question: "In this situation, if these causes are operating, what will be the observed effects?"  The if-then reasoning is reversed in retroduction when we ask an effect-to-cause question: "In this situation, if these effects were observed, what causes could have been operating?"  This reversed question inspires a search in which we do mental experiments over and over, each time "trying out" a different theory in an attempt to produce predictions that match the known observations.  The goal is to find a theory that will pass the reality check, to find a theory that, if true, would explain what has been observed.   { In the diagram above, you can imagine a "feedback cycle" for the three main elements, with each reality-check providing feedback that helps you use OBSERVATIONS to retroductively generate a new THEORY whose new PREDICTIONS will more closely match the old OBSERVATIONS in the next reality-check.  In this way there is an intimate blending of creative generation with critical evaluation. }
      But sometimes the distinction between description and explanation isn't clear, so we also have semi-explanatory theories.

      You can be a scientist, generating your own theory to explain moon phases, by "running a model" for the sun-earth-moon system.  Darken a room, turn on a lamp to be the sun, use one ball for the earth and another ball for the moon.  By looking at the effects of earth's rotation, you should also be able to explain why the sun sets in the west, and why there is a pattern for the times of moonrises and moonsets.

 
      • EXPERIMENTS — Generation & Evaluation
       When scientists generate-and-evaluate an experiment (a controlled lab experiment or uncontrolled field experiment) their main goal is to fill gaps in current knowledge.  Sometimes experiments are done just "to see what will happen," but an experiment (or set of experiments) is usually designed to accomplish a goal — to gather information about experimental systems or techniques, or to resolve anomaly, impress a funding agency, or provide support for an argument, as in a crucial experiment that can distinguish between competing theories.
       To be more efficient so they'll waste less time and resources, scientists can run thought experiments by asking "if we do this, what might happen and what would we learn?"  One aspect of pre-thinking is imagining the questions that will be raised during evaluation — "is the sample large enough and does it accurately represent the whole population?" or "what are the effects of systematic errors and random errors?" or... — and designing experiments to answer these questions.
       New opportunities for experimenting can arise from new events (like an ozone hole) or new discoveries (of old dinosaur bones,...).  Scientists may want to test a new sub-theory or explore its application for a variety of systems.  A new observation technology may allow new experimental systems.  Scientists who are aware and creative, thinking with open-minded imagination, can take advantage of opportunities.
 

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      Scientific Method as Design
      Scientists design (they generate-and-evaluate) theories and experiments. 
      In a page that compares Science and Design and looks at their interactions — such as the technological design-applications of science, and the use of scientific reality checks by a designer who is searching for truth so the products and strategies being designed will have a solid foundation in "the way the world really is" — I define science as "the designing of theories & experiments."
      In their daily work, scientists rarely design large-scale generalized mega-theories, such as the theories of gravity, invariance, or evolution developed by Newton, Einstein, or Darwin.  Instead, usually they are applying generalized theories that already are accepted, in their study of particular experimental situations.  Sometimes they are designing small-scale specialized sub-theories.  For example, a group of chemists might apply generalized theories (atomic theory, quantum mechanics, kinetics, thermodynamics,...) to a particular experimental system, or a collection of systems, in an effort to design a sub-theory that seems to be true (and/or useful) for these systems.
      Or, more commonly, scientists simply accept the mega-theories & sub-theories developed by others, so they can make observations and learn more about nature in the experiments (controlled or uncontrolled) they are designing and running.   { The process of design is similar for a theory, as outlined below, or for an experiment, as described above. }
      Thus, scientists design theories and/or experiments that let them make predictions and/or observations.  The following section is another perspective on scientific method.

 

      Combining two ways to think in Scientific Method:
      Science Mode (using Reality Checks) and
      Design Mode (using Quality Checks)

      Scientists creatively generate a theory, and critically evaluate its quality by using quality-checks in which they compare their GOALS (for the properties of a satisfactory theory) with their OBSERVATIONS (of what the theory's properties are now) and PREDICTIONS (for what they think this theory could be in the future), as shown in the diagram below.  Their GOALS — which are the desired properties of a theory — involve three types of factors: empirical, conceptual, and cultural-personal.

 
      The diagram below shows three comparisons:  scientists compare GOALS (the properties desired for a theory) with OBSERVATIONS (about properties of the theory now) while thinking in design mode, and compare GOALS (desired for theory) with PREDICTIONS (for theory in future) in design mode, and compare reality-based OBSERVATIONS (for a particular system) with theory-based PREDICTIONS (for this system) while thinking in science mode.

      We can think of these comparisons as "checks" for either quality or reality.  While designing a theory (or experiment), scientists use quality checks by comparing their GOALS for a theory's properties with their OBSERVATIONS (or OBSERVATIONS) about this theory's properties.  Usually, the most important observed property of a theory is its performance during reality checks that compare the PREDICTIONS made with a theory (for a particular system-situation) and OBSERVATIONS of reality (in this system-situation).
      The main focus of scientific method (in this page) is reality checks, while quality checks are the main thinking tool in the design method (in another page) that we use for doing almost everything in life, when we design theories (in science and in other areas, including everyday life) and products (things we make and use) and strategies (for a wide variety of strategy-decisions in many areas of life).

 
Above, you've seen a logical-structural analysis of science & design.  But in both types of problem-solving process, in both science and design, the decisions are made by people;  in reality, scientists & designers are motivated and guided by a wide variety of factors that include cultural-personal factors, as described in "Controversy and Complexity" later in this page.
 

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      Does a scientific method exist?

      Is there a scientific method?  If "method" means "a single method, used in the same way by all scientists at all times," the answer is NO.  Some details of methods change with time and culture, and vary from one area of science to another, so there is nothing that could be called The Scientific Method.  But some scientific methods are commonly used by scientists.
      The methods of scientists are designed to be functional, to achieve goals.  For most scientists, the main goal is to find truth.  They want to construct theories that are true, that correspond with reality by correctly describing what really happens in nature.  In a search for true theories, the main thinking tools — the generation and evaluation of theories, using observation, imagination, and logic — are described above.
      But scientists do more than just generate and evaluate theories.  They also design and do experiments, plan big research projects and small daily activities, describe (by writing and talking) their own research, learn (by reading and listening) about the research of others, discuss ideas with other scientists, and more.  Basically, scientists do — mentally and physically — whatever they think will help them achieve their goals.
      The methods of science are flexible, not rigid.  Consider two types of ice skaters.  The sequential actions of a figure skater are precisely planned and, if there are no mistakes, predictable.  By contrast, even though hockey skaters have a strategic plan, the plan is intentionally flexible, with each skater improvising in response to what happens during a game.  The methods used in science are analogous to the flexible "structured improvisation" of a hockey skater, not the rigid choreography of a figure skater.
      These ideas are examined in more detail in a page asking, Is there a scientific method?

 
      Controversy and Complexity
      Scholars, including scientists and those (in philosophy, history, sociology, psychology, and education) who study science, have vigorous discussions about the methods used in science.  Some of the most hotly debated questions are about cultural-personal influences in the process of science, especially in evaluations of scientific theories: Are cultural-personal effects significant, and are they desirable?  Most scientists think these effects should be minimized, but some scholars (especially nonscientists who have adopted a postmodern perspective) think cultural-personal factors should be a part of scientific theory evaluation.
      I claim that empirical factors are usually (but not always) the main factors (but not the only factors) during theory evaluation, that conceptual factors are usually (but not always) scientifically useful, and that cultural-personal factors should be recognized (they do occur) and minimized (because they usually are not scientifically useful).  In what ways, and to what extent, are the process and results of evaluation influenced by conceptual factors and cultural-personal factors?  The influence varies, because it depends on the scientists (and their culture) and the theory.  And it depends on who is answering the question, since this is a topic for hot debate among scientists and (especially) the scholars who study science.
      In most of this page I've emphasized the importance of empirical "reality checks" and the simplicity of science.  But I also recognize the effects of non-empirical factors, and the complexity of science, as outlined below.
 

A Model for Scientific Method (in all of its glorious complexity)
I've developed a "model for the methods of science" that describes nine aspects of what scientists do:
1. Hypothetico-Deductive Logic, and 
    Empirical Factors in Theory Evaluation
2. Conceptual Factors in Theory Evaluation  
3. Cultural-Personal Factors in Theory Evaluation  
4. Theory Evaluation (using critical thinking) 
5. Theory Generation (using creative thinking) 
6. Experimental Design (Generation-and-Evaluation)  
7. Problem-Solving Projects  
8. Thought Styles (cultural and personal) 
9. Mental Operations (in a combination of 
   creative thinking and critical thinking)

      Because my "model for a method" shows the functional relationships between these nine aspects of action, integrating them into a coherent framework, I call it Integrated Scientific Method.  This model, which can be useful for science education, is outlined (visually and verbally) in A Basic Overview of Scientific Method and is examined in depth in A Detailed Overview of Scientific Method which is a condensation of the first half of my PhD dissertation.
      In the page you're now reading, you've seen some of the nine actions.  The main focus has been "reality checks" using hypothetico-deductive logic (1), but you've also seen the process of theory generation (5) and theory evaluation (4) and how a theory is designed using "quality checks" with the criteria for quality based on a combination of empirical factors (1) and conceptual factors (2) and cultural-personal factors (3), and everything is infused with the productive mental operations (9) of creative generation and critical evaluation.  {top of page}
      Learning a simple model, as in this page, is a good way to begin.  But usually it isn't a good place to end.  If you want to understand science more completely, and appreciate it more fully, I encourage you to continue your journey of exploration in the Basic Overview of Integrated Scientific Method (link is above) which will help you learn more about the fascinating complexity of science.  You can also study the hot debates about science (Should scientific method be eks-rated?) or learn about Design Method — you use it for almost everything you do in life! — or compare Science and Design to find their similarities and differences.
      And in an occasionally controversial area, educators (plus parents, school boards,...) have debates about the goals and methods of general education and science education.  In all types of schools — public, private, and home, from K-12 through college — teachers are wondering whether "scientific method" exists and how scientific thinking skills should be taught in the classroom.  They want to offer a quality education that includes scientific concepts plus thinking skills, so students will be motivated to learn, and will learn how to think more often and more effectively, with enthusiasm and skill.  A wide variety of questions — about scientific method, design method, and much more — are explored in the area for thinking skills, and you can see what's available in the overview-sitemap for Design Method & Scientific Method in Education: Developing a Curriculum for Thinking Skills and Problem Solving.