The Duhem–Quine thesis is that it is impossible to test a scientific hypothesis in isolation, because an empirical

Empirical method

The empirical method is generally taken to mean the approach of using a collection of data to base a theory or derive a conclusion in science...

 test of the hypothesis requires one or more background assumptions (also called auxiliary assumptions or auxiliary hypotheses). The hypothesis in question is by itself incapable of making predictions. Instead, the consequences of the hypothesis typically rest on background assumptions from which to derive predictions. This prevents a theory

Theory

The English word theory was derived from a technical term in Ancient Greek philosophy. The word theoria, , meant "a looking at, viewing, beholding", and referring to contemplation or speculation, as opposed to action...

 from becoming conclusively falsified

Falsifiability

Falsifiability or refutability of an assertion, hypothesis or theory is the logical possibility that it can be contradicted by an observation or the outcome of a physical experiment...

 through empirical means if the background assumptions are not proven (since background assumptions sometimes involve one or more scientific theories). For instance, to "disprove" the idea that the Earth

Earth

Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

 is in motion, some people noted that birds did not get thrown off into the sky whenever they let go of a tree branch. That datum

Data

The term data refers to qualitative or quantitative attributes of a variable or set of variables. Data are typically the results of measurements and can be the basis of graphs, images, or observations of a set of variables. Data are often viewed as the lowest level of abstraction from which...

 is no longer accepted as empirical evidence

Evidence

Evidence in its broadest sense includes everything that is used to determine or demonstrate the truth of an assertion. Giving or procuring evidence is the process of using those things that are either presumed to be true, or were themselves proven via evidence, to demonstrate an assertion's truth...

 that the Earth is not moving because we have adopted a different background system of physics

Physics

Physics is a natural science that involves the study of matter and its motion through spacetime, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.Physics is one of the oldest academic...

 that allows us to make different predictions.

Although a bundle of theories (i.e. a theory and its background assumptions) as a whole can be tested against the empirical world and be falsified if it fails the test, the Duhem–Quine thesis says it is impossible to isolate a single hypothesis in the bundle. One solution to the dilemma thus facing scientists is that when we have rational reasons to accept the background assumptions as true (e.g. scientific theories via evidence) we will have rational—albeit nonconclusive—reasons for thinking that the theory tested is probably wrong if the empirical test fails.

Pierre Duhem

As popular as the Duhem–Quine thesis may be in philosophy of science

Philosophy of science

The philosophy of science is concerned with the assumptions, foundations, methods and implications of science. It is also concerned with the use and merit of science and sometimes overlaps metaphysics and epistemology by exploring whether scientific results are actually a study of truth...

, in reality Pierre Duhem

Pierre Duhem

Pierre Maurice Marie Duhem was a French physicist, mathematician and philosopher of science, best known for his writings on the indeterminacy of experimental criteria and on scientific development in the Middle Ages...

 and Willard Van Orman Quine stated very different theses. Duhem believed that only in the field of physics

Physics

Physics is a natural science that involves the study of matter and its motion through spacetime, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.Physics is one of the oldest academic...

can a single individual hypothesis not be isolated for testing. He says in no uncertain terms that experimental theory in physics is not the same as in fields like physiology

Physiology

Physiology is the science of the function of living systems. This includes how organisms, organ systems, organs, cells, and bio-molecules carry out the chemical or physical functions that exist in a living system. The highest honor awarded in physiology is the Nobel Prize in Physiology or...

 and certain branches of chemistry

Chemistry

Chemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties. Chemistry is concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds....

. Also, Duhem's conception of "theoretical group" has its limits, since he states that not all concepts are connected to each other logically. He did not include at all a priori disciplines such as logic

Logic

In philosophy, Logic is the formal systematic study of the principles of valid inference and correct reasoning. Logic is used in most intellectual activities, but is studied primarily in the disciplines of philosophy, mathematics, semantics, and computer science...

 and mathematics

Mathematics

Mathematics is the study of quantity, space, structure, and change. Mathematicians seek out patterns and formulate new conjectures. Mathematicians resolve the truth or falsity of conjectures by mathematical proofs, which are arguments sufficient to convince other mathematicians of their validity...

 within the theoretical groups in physics, since they cannot be tested.

Willard Van Orman Quine

Quine, on the other hand, in "Two Dogmas of Empiricism

Two Dogmas of Empiricism

W. V. Quine's paper Two Dogmas of Empiricism, published in 1951, is one of the most celebrated papers of twentieth century philosophy in the analytic tradition. According to Harvard professor of philosophy Peter Godfrey-Smith, this "paper [is] sometimes regarded as the most important in all of...

", presents a much stronger version of underdetermination

Underdetermination

In scientific theory, underdetermination refers to situations where the evidence available is insufficient to identify which belief we should hold about that evidence...

 in science. His theoretical group embraces all of human knowledge, including mathematics and logic. He contemplated the entirety of human knowledge as being one unit of empirical significance. Hence all our knowledge, for Quine, would be epistemologically no different from ancient Greek gods, which were posited in order to account for experience. Quine even believed that logic and mathematics can also be revised in light of experience, and presented quantum logic

Quantum logic

In quantum mechanics, quantum logic is a set of rules for reasoning about propositions which takes the principles of quantum theory into account...

 as evidence for this. Years later he retracted this position; in his book Philosophy of Logic, he said that to revise logic would be essentially "changing the subject". In classic logic, connectives are defined according to truth values. The connectives in a multi-valued logic, however, have a different meaning than those of classic logic. As for quantum

Quantum

In physics, a quantum is the minimum amount of any physical entity involved in an interaction. Behind this, one finds the fundamental notion that a physical property may be "quantized," referred to as "the hypothesis of quantization". This means that the magnitude can take on only certain discrete...

logic, it is not even a logic based on truth values, so the logical connectives lose the original meaning of classic logic. Quine also notes that deviant logics usually lack the simplicity of classic logic, and are not so fruitful.