Peirce: a useful hypothesis opens an inquiry

Where does an explanation come from when something surprises us? Charles Sanders Peirce, an American philosopher and scientist who lived from 1839 to 1914, made inquiry central to his thinking. His philosophy extended well beyond this question, but following it offers a concrete way into his work: before we can test an answer, we need a possible answer to put to the test. [1]

Peirce called the reasoning that proposes an explanatory hypothesis abduction. We notice an unexpected fact and imagine a situation that would make it understandable. This is a possibility to investigate, not a demonstrated conclusion: explaining an observation does not establish that the explanation is true. [2][4]

In Peirce's mature account, abduction works alongside two further stages. Deduction draws consequences we should expect from the hypothesis; induction includes experimental testing and the assessment of results. Proposing, deriving consequences and checking are therefore distinct activities. If observations conflict with predictions, inquiry must be able to return to its hypotheses. Knowing the name of a type of reasoning does not make its user infallible. [3]

Here is an example invented by the editors. We find the inside windowsill wet. Perhaps rain came through the window; perhaps someone spilled water while watering a plant. Both ideas might explain what we see. Write them on two separate lines, leaving a third line for the observation: the windowsill is wet. If we immediately wrote that the window had let rain in, we would already have slipped one explanation into the initial description. [2]

Continue the same editorial example. Ask whoever was home whether they watered the plant and look at where the traces of water continue. Note what each hypothesis would lead us to look for, alongside what we actually find. An open window alone does not choose between the two stories for us. We might have overlooked another cause or found clues consistent with both. The exercise aims to make the process visible: observation, proposal, checking and possible revision, without rewarding the first answer simply because it came quickly. [3]

A historical qualification matters too. Peirce developed his ideas over decades: this introductory outline does not cover every stage of his thinking. Nor does his abduction simply match the present-day formula of inference to the best explanation. Our focus here is the moment when a possibility becomes worth investigating, before determining how well it stands up to testing. [1][2]