History of scientific method

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

Early philosophical tradition

Ancient Greece, towards the middle of the 5th century BC was advanced in fields from architecture to transport. Also some of the tools of modern scientific tradition were already well established. In Protagoras (318d-f), Plato mentions the teaching of arithmetic, astronomy and geometry in schools. Among the Ancient Greeks were those who sought a knowledge that was qualitatively superior to the know-how of the artisans of their time. The philosophers had begun afresh the project of building knowledge from foundations that were mostly freed from the constraints of everyday phenomena and common sense.

Aristotlian science

For Aristotle, universal truths can be known from particular things via induction. To some extent then, Aristotle reconciles abstract thought with observation, although it would be misleading to imply that Aristotelian science is empirical in form. Indeed, Aristotle did not accept that knowledge acquired by induction could rightly be counted as scientific knowledge. Nevertheless, induction was a necessary preliminary to the main business of scientific enquiry, providing the primary premises required for scientific demonstrations.

Aristotle largely ignored inductive reasoning in his treatment of scientific enquiry. To make it clear why this is so, consider his statement in 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."

It was therefore the work of the scientist to demonstrate universal truths and to discover their causes. 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 universal truths from those already established.

Aristotle developed a complete normative approach to scientific enquiry involving the syllogism which is discussed at length in his Posterior Analytics. Perhaps most striking today, where the use of mathematics is common place in the physical sciences, would be the admonition that theorems of any one science not be demonstrated by means of another science.

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. This leads to the question of how the primary premises are arrived at, and as we have already mentioned, Aristotle allowed that induction would be required for this task.

Towards the end of Posterior Analytics, Aristotle discusses knowledge 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 leaves room for doubt regarding the nature and extent of his empiricism. In particular, it seems that Aristotle considers sense-perception only as a vehicle for knowledge through intuition. Induction is not afforded the status of scientific reasoning, and so it is left to intuition to provide a solid foundation for Aristotle’s science. With that said, Aristotle brings us somewhat closer to an empirical science than his predecessors.

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. During the Middle Ages, Islamic philosophy developed and was often pivotal in scientific debates–key figures were usually scientists and philosophers.

The prominent Arab-Persian Muslim scientist Alhazen used the scientific method to obtain the results in his book Optics. In particular, he combined observations and rational arguments to show that his intromission theory of vision, where light is emitted from objects rather than from the eyes, influenced by Aristotle's early ideas, was scientifically correct, and that the emission theory of vision supported by Ptolemy and Euclid was wrong.

During the 12th century, ideas on 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, 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 the manner in which he conducted his experiments in precise detail so that others could reproduce and independently test his results.

Scientific revolution methodologists

Despite being initially seen as a possible threat to Christian orthodoxy, Aristotle’s ideas became a framework for critical debate beginning with absorption of the Aristotelian texts into the university curriculum in the first half of the thirteenth century. Contributing to this was the success of medieval theologians in reconciling Aristotelian philosophy with Christian theology. Within the sciences, medieval philosophers were not afraid of disagreeing with Aristotle on many specific issues, although their disagreements were stated within the language of Aristotelian philosophy. All medieval natural philosophers were Aristotelians, but "Aristotelianism" had become a somewhat 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 seventeenth 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 writing his first major treatise on proper scientific and philosophical thinking, the unfinished Rules for the Direction of the Mind where he hoped to overthrow the Aristotelian system and establish himself as the sole architect of a new system of guiding principles for scientific research.

This work was continued and clarified 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, a number 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 the methods of study he selected were in keeping with Aristotelian teachings. Whereas Aristotle thought that a science should be demonstrated from first principles, Galileo had used experiments as a research tool. Galileo nevertheless presented his treatise in the form of mathematical demonstrations without reference to experimental results. It is important to understand that this in itself was a bold and innovative step in terms of scientific method. The usefulness 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 himself 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 dialogues 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.

As an example, in the dramatic dialogue entitled Third Day from his Two New Sciences, Galileo has the characters of the dialogue discuss an experiment involving two free falling objects of differing weight. An outline of the Aristotelian view is offered by the character Simplicio. For this experiment he expects that "a body which is ten times as heavy as another will move ten times as rapidly as the other". The character Salviati, representing Galileo's persona in the dialogue, replies by voicing his doubt 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 stone apart, the heavier object should in fact fall with a speed greater than that of either stone. From this contradiction, Salviati concludes that Aristotle must in fact 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 had shied away from the role of experimenter, the opposite can be said for 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 employed by 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 his method would produce certain knowledge rather than tentatively justify adherence to knowledge claims. Bacon explains how his method is applied in his Novum Organum (published 1620). In an example he gives on the examination of the nature of heat, Bacon creates two tables, the first of which he names "Table of Essence and Presence", enumerating the many various circumstances under which we find heat. In the other table, labelled "Table of Deviation, or of Absence in Proximity", he lists circumstances which bare resemblance to those of the first table except for the absence of heat. From an analysis of, what he calls, 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 experimentation played in this process was two-fold. The most laborious job of the scientist would be to gather the facts, or 'histories', required to create the tables of presence and absence. Such histories would document a mixture of 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. Despite this he did not make any great scientific discoveries during his lifetime. This may be because he was not the most able experimenter. It may also be because hypothesizing plays 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 left for guess work 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" (Novum Organum XCVI).

Preamble to scientific method

Both Bacon and Descartes wanted to provide a firm foundation for scientific thought that avoided the deceptions of the mind and senses. Bacon envisaged that foundation as essentially empirical, whereas Descartes' provides a metaphysical foundation for knowledge.

If there were any doubts about the direction in which scientific method would develop, they were set to rest by the success of Isaac Newton. He outlines his four "rules of reasoning" in the Principia, which became a model that other sciences sought to emulate,

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.

But Newton also left an admonition about a theory of everything:

"To explain all nature is too difficult a task for any one man or even for any one age. 'Tis much better to do a little with certainty, and leave the rest for others that come after you, than to explain all things."

Some methods of reasoning were systematized by John Stuart Mill's Canons, which are five explicit statements of what can be discarded and what can be kept while building a hypothesis. George Boole and William Stanley Jevons also wrote on the principles of reasoning.

Integrating deductive and inductive method

Attempts to systematize a scientific method were confronted in the mid-18th century by the problem of induction, a positivist logic formulation which, in short, asserts that nothing can be known with certainty except what is actually 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 are unable to justify inductive reasoning itself by appealing to its past success. Hume's arguments, of course, came on the heels of many, many centuries of excessive speculation upon excessive speculation not grounded in empirical observation and testing. Although Hume's radically skeptical arguments were convincingly refuted and ultimately superseded by Immanuel Kant's Critique of Pure Reason in the late 18th century, Hume's brilliantly formatted arguments continued to hold a strong lingering influence on the consciousness of the educated classes 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 proposed a schema that would turn out to have considerable influence in the further development of scientific method generally. Peirce's work quickly accelerated the progress on several fronts. Firstly, speaking in broader context in "How to Make Our Ideas Clear" (1878) [1], Peirce outlined an objectively verifiable method to test the truth of putative knowledge on a way that goes beyond mere foundational alternatives, focusing upon both Deduction and Induction. He thus placed induction and deduction in a complimentary rather than competitive context (the latter of which had been the primary trend at least since David Hume a century before). Secondly, and of more direct importance to scientific method, Peirce put forth the basic schema for hypothesis-testing that continues to prevail today. Extracting the theory of inquiry from its raw materials in classical logic, he refined it in parallel with the early development of symbolic logic to address the then-current problems in scientific reasoning. Peirce examined and articulated the three fundamental modes of reasoning that play a role in scientific inquiry today, the processes that are currently known as abductive, deductive, and inductive inference. Thirdly, he played a major role in the progress of symbolic logic itself — indeed this was his primary specialty.

Karl Popper (1902-1994) is generally credited with providing a context for major improvements in scientific method in the mid-to-late 20th century. Beginning in the 1930s and with increased vigor after World War II, he argued that a hypothesis must be falsifiable and, following Peirce and others, that science would best progress using deductive reasoning as its primary emphasis, known as critical rationalism. His astute formulations of logical procedure helped to reign in the excessive use of inductive speculation upon inductive speculation, and also helped to strengthen the conceptual foundation for today's peer review procedures.

Critics of Popper, chiefly Thomas Kuhn, Paul Feyerabend and Imre Lakatos, rejected the idea that there exists a single method that applies to all science and could account for its progress. Indeed most scientists would agree. There remain, nonetheless, certain core principles that are the foundation of scientific inquiry today. (see also: scientific method)