This prevents a theory from becoming conclusively falsified through empirical means if the background assumptions are not proven (since background assumptions sometimes involve one or more scientific theories, and scientific theories are never strictly proven).
It is always possible to reject an apparently falsifying observation by claiming that only one of its underlying assumptions is false; since there are an indeterminate number of such assumptions, any observation can potentially be made compatible with any theory.
So it is quite valid to use a theory to reject an observation.
Similarly, a theory consists of some indeterminate conjunction of hypotheses, In words, the failure of some theory implies the failure of at least one of its underlying hypotheses.
It is always possible to resurrect a falsified theory by claiming that only one of its underlying hypotheses is false; again, since there are an indeterminate number of such hypotheses, any theory can potentially be made compatible with any particular observation.
Also, Duhem's conception of "theoretical group" has its limits, since he states that not all concepts are connected to each other logically.
What Is Duhem Holism Thesis
He did not include at all a priori disciplines such as logic and mathematics within the theoretical groups in physics, since they cannot be tested experimentally.
Their theses also blurred the sharp distinction between theories in the natural sciences and those in the social and human sciences, distinctions that had been in question under hermeneutics.
The Duhem–Quine thesis (also called the Duhem–Quine problem) states that it is impossible to test a scientific hypothesis in isolation, because an empirical test of the hypothesis requires one or more background assumptions (also called auxiliary assumptions or auxiliary hypotheses).
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.