What Is the Scientific Method?
The scientific method combines experiment and mathematical reasoning. It developed through the Scientific Revolution in the work of Bacon, Descartes, Galileo, and Newton.
What Is the Scientific Method?
The phrase “the scientific method” describes the general procedure by which natural philosophers and scientists investigate the natural world: careful observation, controlled experiment, the construction of hypotheses, the deduction of consequences from those hypotheses, and the comparison of those consequences with the phenomena. The method, as we know it today, is a product of the Scientific Revolution. It was developed in the seventeenth century, in the work of Francis Bacon, René Descartes, Galileo Galilei, and Isaac Newton, and it was institutionalized in the Royal Society, the Académie des Sciences, and the research universities of the eighteenth and nineteenth centuries. This page follows the growth of the method through the period.
What the Method Is
In its modern form, the scientific method is a procedure for the investigation of natural phenomena that combines empirical observation with mathematical reasoning. It has several typical steps:
- Observation. The investigation begins with careful observation of some natural phenomenon — the motion of the planets, the behavior of falling bodies, the spread of disease.
- Hypothesis. The investigator formulates a hypothesis that explains the phenomenon — a proposed law or mechanism that, if true, would account for the observed facts.
- Deduction. From the hypothesis, the investigator deduces specific predictions about what should be observed under specified conditions.
- Experiment. The investigator designs and performs experiments to test those predictions.
- Confirmation or revision. If the predictions are confirmed, the hypothesis is provisionally accepted; if not, the hypothesis is revised or rejected. This account is, of course, a simplification. In practice, scientific method is messier, more flexible, and less algorithmic than the textbook account suggests. Yet the basic combination of observation, hypothesis, deduction, and experiment is recognizable in the actual practice of science from the seventeenth century onward.
Bacon’s Inductive Tables
The first explicit program for a new scientific method was that of Francis Bacon (1561–1626), the English philosopher and Lord Chancellor. In his Novum Organum (1620), Bacon argued that the Aristotelian-Scholastic logic was inadequate to the task of natural philosophy. The Aristotelian approach, in his view, was too ready to construct theories on the basis of inadequate observation, and too confident in the conclusions drawn by deductive reasoning from those theories. Bacon’s proposed remedy was a careful, inductive method. He distinguished three kinds of “tables” or collections of instances:
- Tables of presence. Collections of instances in which the phenomenon under investigation is observed to occur.
- Tables of absence. Collections of instances in which the phenomenon is observed to be absent, even where one might expect it to be present.
- Tables of degrees. Collections of instances in which the phenomenon is observed to occur in greater or lesser degree, with corresponding variations in the proposed cause. By comparing the three kinds of tables, the investigator could, in Bacon’s view, gradually ascend to the true cause of the phenomenon. The method was laborious and demanding, but it was designed to avoid the errors of the Aristotelian tradition. In practice, Bacon’s method was not widely adopted in the form he proposed. It was too mechanical to be applied in most cases, and it underestimated the role of hypothesis and theory in guiding observation. Yet Bacon’s program had an enormous influence on the growth of the experimental tradition, especially in England. The Royal Society of London, founded in 1660, was deeply Baconian in its rhetoric and, to a considerable extent, in its practice.
Descartes and Deduction
René Descartes (1596–1650) advanced a strikingly different method, in which deduction, rather than induction, was central. In his Discourse on Method (1637) and Meditations (1641), Descartes proposed that genuine knowledge must be grounded in clear and distinct ideas, perceived by the mind, and that the proper method of inquiry is the deduction of conclusions from those ideas by rigorous logical reasoning. Descartes’s method had four rules:
- Accept nothing as true that is not known to be so.
- Divide each difficulty into as many parts as possible.
- Begin with the simplest and most easily known objects, and ascend step by step to the knowledge of the most complex.
- Make enumerations so complete, and reviews so general, that nothing is omitted. The model for this method was mathematics, and especially the deductive structure of geometry. Descartes sought to make the whole of natural philosophy into a deductive system modeled on mathematics, deriving the laws of nature from the clear and distinct idea of extension and explaining the physical world as a system of corpuscles in motion. Descartes’s method was enormously influential in continental Europe, especially in France and the Netherlands. It inspired a generation of natural philosophers, including Christiaan Huygens and (in his earlier years) Leibniz. It also provoked a sustained counter-tradition in England, especially in the work of the Royal Society, which was more Baconian in spirit. The contrast between the two methods is examined in detail in the article on Rationalism vs Empiricism.
Galileo’s Combination of Experiment and Mathematics
Galileo Galilei (1564–1642) is often credited with the most successful combination of the empirical and the rationalist approaches, and his work on motion is often presented as the model of the new method. In his Two New Sciences (1638), Galileo reported a series of experiments on the motion of falling bodies, the motion of pendulums, and the motion of projectiles. The experiments were carefully designed, with controlled conditions, and the results were stated in mathematical form. Galileo’s method was a synthesis of the Baconian and Cartesian approaches. From Bacon, Galileo took the insistence on direct investigation of nature, on careful observation, and on the use of experiment. From Descartes and the mathematical tradition, he took the conviction that the proper aim of natural philosophy is the discovery of mathematical laws, and that the right way to formulate those laws is in the language of geometry. The combination was remarkably productive. Galileo’s law of falling bodies — that the distance fallen is proportional to the square of the time elapsed — was stated in mathematical form, derived from carefully designed experiments, and used to predict the behavior of bodies in a variety of conditions. The example set the agenda for the new science, and it remains the model of the scientific method to this day. The story of Galileo’s method is told in the articles on the trial of Galileo and on the key dates of the revolution.
Newton’s Rules of Reasoning
The most influential articulation of the scientific method in the late seventeenth century was Isaac Newton’s Rules of Reasoning in Philosophy, prefixed to the Principia Mathematica (1687) and the Opticks (1704). The four rules were:
- Rule 1. We are to admit no more causes of natural things than such as are both true and sufficient to explain their appearances.
- Rule 2. Therefore to the same natural effects we must, as far as possible, assign the same causes.
- Rule 3. The qualities of bodies, which admit neither intensification nor remission of degree, and which are found to belong to all bodies within the reach of our experiments, are to be esteemed the universal qualities of all bodies whatsoever.
- Rule 4. In experimental philosophy we are to look upon propositions inferred by general induction from phenomena as accurately or very nearly true, notwithstanding any contrary hypotheses that may be imagined, till such time as other phenomena occur, by which they may either be made more accurate, or liable to exceptions. These rules defined a sophisticated middle path between naive induction and dogmatic deduction. They acknowledged that science must be grounded in phenomena (the empirical commitment), that the same causes are to be assigned to the same effects (a kind of parsimony principle, now known as Occam’s razor), and that the propositions of natural philosophy are to be taken as (provisionally) true on the basis of their agreement with phenomena (a fallibilist commitment to empirical confirmation). Newton’s method, as embodied in the Principia, was the most successful application of the new method to date. The book deduced, from a small number of empirically established laws, a wide range of phenomena: the motion of the planets and their moons, the behavior of comets, the rise and fall of the tides, the precession of the equinoxes, the motion of projectiles, the behavior of fluids. The success of the Principia helped to establish the model of mathematical natural philosophy that would dominate physics for the next two centuries. See the article on the Principia Mathematica.
The Institutionalization of the Method
The scientific method was not only developed in the works of individual philosophers; it was also institutionalized in the new scientific societies of the seventeenth century. The Accademia del Cimento in Florence (1657–1667), the Royal Society of London (1660–), and the Académie Royale des Sciences in Paris (1666–) provided a social context in which the new method could be practiced and refined. The societies met regularly to witness and discuss experiments, and they published reports of those experiments in the Philosophical Transactions (from 1665), the Journal des sçavans (from 1665), and the Histoire de l’Académie Royale des Sciences (from 1699). The publications established a community of inquiry that transcended national boundaries and that defined the norms of the new science: the importance of replication, the value of quantitative description, the commitment to direct investigation of nature.
The Method in the Long Run
The scientific method developed during the Scientific Revolution became the dominant model for the investigation of nature in the eighteenth, nineteenth, and twentieth centuries. The combination of empirical observation, mathematical description, and the construction and testing of hypotheses was applied to electricity and magnetism, to chemistry, to geology, to biology, and eventually to the atom and the cosmos. The method was, of course, refined and developed in the process — the great names of nineteenth-century science, from Lavoisier and Dalton to Darwin and Maxwell, used the basic framework established in the seventeenth century, but added new methods of experiment, new mathematical techniques, and new standards of evidence. The story of these developments is part of the longer history of the philosophy of science, examined in the page on Philosophy of Science and in the broader Scientific Revolution overview. For the contrast between the empirical and the rationalist approaches, see the article on Rationalism vs Empiricism. For the more general background, see the article on What Is Empiricism and Why Did It Matter?.