History of scientific method

The history of scientific method is inseparable from the history of science itself.

Early philosophical tradition

By the middle of the 5th century BCE, Ancient Greece was advanced in many areas, from architecture to transport; some of the tools of science were already well established, and Plato (c. 427–347 BCE) mentions the teaching of arithmetic, astronomy and geometry in schools. The philosophers of Ancient Greece had begun the project of building knowledge from foundations that were mostly freed from the constraints of everyday phenomena and common sense.

Aristotelian science

Plato's pupil, Aristotle (384–322 BCE) is regarded as the originator of many different areas of scientific inquiry. Aristotle considered that universal truths could be discovered by careful observation of the many particular instances of those truths, a process of reasoning known as induction. To some extent then, Aristotle reconciled abstract thought with observation, but it would be misleading to imply that Aristotelian science is empirical. Indeed, Aristotle did not accept that knowledge acquired by induction could rightly be counted as "scientific" knowledge. Nevertheless, induction was a necessary preliminary to scientific enquiry, providing the primary premises required for scientific demonstrations.

It was the work of the scientist not merely to demonstrate universal truths but also to discover their causes. As Aristotle explains in his Posterior Analytics,

"We suppose ourselves to possess unqualified scientific knowledge of a thing, as opposed to knowing it in the accidental way in which the sophist knows, when we think that we know the cause on which the fact depends, as the cause of that fact and of no other, and, further, that the fact could not be other than it is."

While induction was sufficient for discovering universals by generalization, it did not succeed in identifying causes. The tool Aristotle chose for this was deductive reasoning in the form of syllogisms. Using the syllogism, scientists could infer new truths from those already established.

Aristotle developed a complete, normative approach to scientific enquiry involving the syllogism. A difficulty with this scheme lay in showing that derived truths have solid primary premises. Aristotle would not allow that demonstrations could be circular; supporting the conclusion by the premises, and the premises by the conclusion. Nor would he allow an infinite number of middle terms between the primary premises and the conclusion. So how were the primary premises are arrived at? Towards the end of Posterior Analytics, Aristotle argues that knowledge of the primary premises is imparted by induction.,

"Thus it is clear that we must get to know the primary premises by induction; for the method by which even sense-perception implants the universal is inductive. […] it follows that there will be no scientific knowledge of the primary premises, and since except intuition nothing can be truer than scientific knowledge, it will be intuition that apprehends the primary premises. […] If, therefore, it is the only other kind of true thinking except scientific knowing, intuition will be the originative source of scientific knowledge."

The account raises questions about Aristotle's empiricism. In particular, he considers sense-perception only as a vehicle for knowledge obtained via intuition. Induction is not afforded the status of scientific reasoning, and so it is left to the intuition to provide a solid foundation for Aristotle’s science. Nevertheless, Aristotle comes closer to an empirical science than his predecessors did.

Emergence of inductive method

Elements of a modern scientific method are found in early Muslim philosophy, in particular, using experiments to distinguish between competing scientific theories and a general belief that knowledge reveals nature honestly. In the Middle Ages, Islamic philosophy developed and was often pivotal in scientific debates–key figures were usually scientists and philosophers.

The Arab physicist Abu Ali Hasan Ibn al-Haitham (more often known in the West as Alhazen) (965-1040 CE) was particularly influential. His work on optics, Kitab-al-Manadhirn, which contained a careful examination of the laws of reflection and refraction, was translated into Latin in the Middle Ages. An important observation in that work led Alhazen to propose that the eyes receive light reflected from objects, rather than emanating light themselves, contradicting contemporary beliefs, including those of Ptolemy and Euclid. The way in which Alhazen combined observations and rational arguments had a great influence on Roger Bacon and Johannes Kepler in particular.

In the 12th century, ideas of scientific method, including those of Aristotle and Alhazen, were introduced to medieval Europe through Latin translations of Arabic and Greek texts and commentaries. Robert Grosseteste's commentary on the Posterior Analytics places Grosseteste among the first scholastic thinkers in Europe to fully understand Aristotle's vision of the dual path of scientific reasoning. Concluding from particular observations into a universal law, and then back again: from universal laws to prediction of particulars. Grosseteste called this "resolution and composition". Further, Grosseteste said that both paths should be verified through experimentation in order to verify the principals.

Roger Bacon(c. 1214–1294), a Franciscan friar working under the tuition of Grosseteste, was inspired by the writings of Muslim scientists (particularly Alhazen) who had preserved and built upon Aristotle's portrait of induction. In his enunciation of a method, Bacon described a repeating cycle of observation, hypothesis, experimentation, and the need for independent verification. He recorded his experiments in precise detail so that others could reproduce and independently test his results.

Scientific revolution methodologists

Despite being initially seen as a threat to Christian orthodoxy, Aristotelian texts became absorbed into the university curriculum in the first half of the 13th century, as medieval theologians succeeded in reconciling Aristotelian philosophy with Christian theology. Within the sciences, medieval philosophers disagreed with Aristotle on many specific issues, but their disagreements were stated within the language of Aristotelian philosophy. All medieval natural philosophers were Aristotelians, but this was a broad and flexible concept. With the end of Middle Ages, the Renaissance rejection of medieval traditions coupled with an extreme reverence for classical sources led to a recovery of other ancient philosophical traditions, especially the teachings of Plato. By the 17th century, those who clung dogmatically to Aristotle's teachings were faced with several competing approaches to nature.

Descartes' Aristotelian ambitions

In 1619, René Descartes began his first major treatise on scientific and philosophical thinking, the unfinished Rules for the Direction of the Mind where he hoped to overthrow the Aristotelian system in favour of a new system of guiding principles for scientific research. This work was continued in his 1637 treatise, Discourse on Method and in his 1641 Meditations. Descartes describes the intriguing and disciplined thought experiments he used to arrive at the idea we instantly associate with him: I think therefore I am (cogito ergo sum).

From this foundational thought, Descartes finds proof of the existence of a God who, possessing all possible perfections, will not deceive him provided he resolves "[…] never to accept anything for true which I did not clearly know to be such; that is to say, carefully to avoid precipitancy and prejudice, and to comprise nothing more in my judgment than what was presented to my mind so clearly and distinctly as to exclude all ground of methodic doubt."

This rule allowed Descartes to progress beyond his own thoughts and judge that there exist extended bodies outside of his own thoughts. Descartes published seven sets of objections to the Meditations from various sources along with his replies to them. Despite his apparent departure from the Aristotelian system, some of his critics felt that Descartes had done little more than replace the primary premises of Aristotle with those of his own. Descartes says as much himself in a letter written in 1647 to the translator of Principles of Philosophy,

"a perfect knowledge [...] must necessarily be deduced from first causes [...] we must try to deduce from these principles knowledge of the things which depend on them, that there be nothing in the whole chain of deductions deriving from them that is not perfectly manifest."

And again, some years earlier, speaking of Galileo's physics in a letter to his friend and critic Mersenne from 1638,

"without having considered the first causes of nature, [Galileo] has merely looked for the explanations of a few particular effects, and he has thereby built without foundations."

Descartes failed to produce scientific results comparable to those of his contemporaries, and so it is not here that we find Descartes primary contribution to science. His work in analytic geometry however, was a necessary precedent to differential calculus and instrumental in bringing mathematical analysis to bear on scientific matters.

Galileo

Modern replica of Galileo's inclined plane experiment: The distance covered by a uniformly accelerated body is proportional to the square of the time elapsed

During the period of religious conservativism brought about by the Reformation and Counter-Reformation, Galileo Galilei unveiled his new science of motion. Neither the contents of Galileo’s science, nor his methods of study were in keeping with Aristotelian teachings. Whereas Aristotle thought that a science should be demonstrated from first principles, Galileo used experiments as a research tool. Galileo nevertheless presented his treatise in the form of mathematical demonstrations without referring to experimental results. This was a bold and innovative step: the value of mathematics in obtaining scientific results was far from obvious. This is because mathematics did not lend itself to the primary pursuit of Aristotelian science: the discovery of causes.

Whether it is because Galileo was realistic about the acceptability of presenting experimental results as evidence or because he had doubts about the epistemological status of experimental findings is not known. Nevertheless, it is not in his Latin treatise on motion that we find reference to experiments, but in his supplementary dialogues written in the Italian vernacular. In these, experimental results are given, although Galileo may have found them inadequate for persuading his audience. 'Thought experiments' showing logical contradictions in Aristotelian thinking, presented in the skilled rhetoric of Galileo's dialogue were further enticements for the reader.

For example, in the dramatic dialogue entitled Third Day from his Two New Sciences, Galileo's two characters, Simplicio and Salviati, discuss an experiment involving two free-falling objects of differing weight. The Aristotelian view is outlined by Simplicio, who expects that "a body which is ten times as heavy as another will move ten times as rapidly as the other". Salviati, representing Galileo's persona, replies by doubting that Aristotle ever attempted the experiment. Salviati then asks the two other characters of the dialogue to consider a thought experiment whereby two stones of differing weights are tied together before being released. Following Aristotle, Salviati reasons that "the more rapid one will be partly retarded by the slower, and the slower will be somewhat hastened by the swifter". But this leads to a contradiction, since the two stones together make a heavier object than either apart, the heavier object should fall with faster than either stone. From this contradiction, Salviati concludes that Aristotle must be wrong and the objects will fall at the same speed regardless of their weight, a conclusion that is borne out by experiment.

Francis Bacon's eliminative induction

If Galileo shied away from the role of experimenter, the opposite can be said of his English contemporary Francis Bacon. Bacon attempted to describe a rational procedure for establishing causation between phenomena based on induction. It was, however, a radically different form of induction to that of the Aristotelians. As Bacon put it,

"[A]nother form of induction must be devised than has hitherto been employed, and it must be used for proving and discovering not first principles (as they are called) only, but also the lesser axioms, and the middle, and indeed all. For the induction which proceeds by simple enumeration is childish."

Bacon's method relied on experimental histories to eliminate alternative theories. In this sense it is a precursor to Popper's falsificationism. However, Bacon believed that his method would produce certain knowledge rather than tentatively justify adherence to knowledge claims. Bacon explains his method in his Novum Organum, published in 1622. In an example he gives on examining the nature of heat, Bacon creates a "Table of Essence and Presence", which enumerates the various circumstances under which we find heat, and a "Table of Deviation, or of Absence in Proximity", which lists circumstances that resemble those of the first table except for the absence of heat. By analysing the natures (light emitting, heavy, colored etc.) of the items in these lists we are brought to conclusions about the form nature, or cause, of heat. Those natures which are always present in the first table, but never in the second are deemed to be the cause of heat.

The role of experiments in this process was two-fold. The most laborious job of the scientist is to gather the facts, or 'histories', needed to create the tables of presence and absence. Such histories would include both common knowledge and experimental results. Secondly, experiments of light, or, as we might say, crucial experiments would be needed to resolve any remaining ambiguities over causes.

Bacon showed an uncompromising commitment to experimentation, although he made no great scientific discoveries himself, perhaps because he was not the most able experimenter. It may also be because hypotheses play only a small role in Bacon's method compared to modern science. Hypotheses, in Bacon's method, are supposed to emerge during the process of investigation, with little room for guesswork and creativity. Neither did he attribute much importance to mathematical speculation "which ought only to give definiteness to natural philosophy, not to generate or give it birth" .

Isaac Newton

In England, shortly after Bacon’s death, the Royal Society was formed; its founders inspired by Bacon’s unfinished New Atlantis, with its utopian vision of a scientifically advanced civilization. If there were any doubts about the direction in which scientific method would develop, they were set to rest by the success of a Royal Society fellow, Isaac Newton. In his Principia Newton outlined four "rules of reasoning",

1. We are to admit no more causes of natural things than such as are both true and sufficient to explain their appearances.
2. Therefore to the same natural effects we must, as far as possible, assign the same causes.
3. The qualities of bodies, which admit neither intension nor remission of degrees, 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.
4. In experimental philosophy we are to look upon propositions collected by general induction from phænomena as accurately or very nearly true, notwithstanding any contrary hypotheses that may be imagined, till such time as other phænomena occur, by which they may either be made more accurate, or liable to exceptions.

As a note to the last rule, Newton writes, "This rule we must follow, that the argument of induction may not be evaded by hypotheses." Thus, while Newton helped to cement the practice of experimental science, he also retained the idea that scientific knowledge is a consequence of applying the correct method.

Integrating deductive and inductive method

Attempts to systematize a scientific method were confronted in the mid-18th century by the problem of induction, which asserts that nothing can be known with certainty except what has actually been observed. David Hume took empiricism to the skeptical extreme; among his positions was that there is no logical necessity that the future should resemble the past, thus we cannot justify inductive reasoning itself by appealing to its past success. Hume's arguments came on the heels of many centuries of speculation not grounded in empirical testing. Although Hume's skeptical arguments were refuted and ultimately superseded by Immanuel Kant's Critique of Pure Reason in the late 18th century, his arguments continued to have a strong influence for the better part of the 19th century. Thus the argument at the time tended to focus on whether or not the inductive method was valid.

In the late 19th century, Charles Sanders Peirce, outlined an objective way to test the truth of putative knowledge that uses both Deduction and Induction. Peirce proposed the basic schema for hypothesis-testing that prevails today. Extracting the theory of inquiry from classical logic, he refined it with the early development of symbolic logic to address problems about scientific reasoning. He also articulated the three fundamental modes of reasoning that play a role in scientific inquiry, the processes of abductive, deductive, and inductive inference.

Karl Popper (1902-1994) is generally credited with stimulating major improvements in scientific method in the mid-to-late 20th century. He argued that a good hypothesis must be, in principle, falsifiable. He argued that inductive inferences were inevitably logically unsound, and that experiments that aimed at "verification" or "confirmation" of hypotheses provided at best weak evidence; instead he argued that scientific experiments should be designed as attempts at falsifying bold hypotheses. by attempting to disprove predictions derived from the hypotheses by deductive reasoning, a philosophy that he described as critical rationalism. His astute formulations of logical procedure also helped to strengthen the conceptual foundation for today's peer review procedures.

Critics of Popper, notably Thomas Kuhn, Paul Feyerabend and Imre Lakatos, rejected for different reasons, the idea that Popper's view of the scientific method applies to all science. There remain, nonetheless, certain core principles that are the foundation of scientific inquiry today. (see also: scientific method)