2. The structure of scientific inquiry
The following ideas have also been explicated to some degree above but they deserve more attention. The structure of scientific inquiry follows the basic rules of scientific attitude, for example that sham reasoning is to be avoided (CP 1.57), as presented above. Some ideas, however, are very important. These include the processes of inference for example.
In addition to the traditional forms of inference (induction and deduction), Peirce formulated a third kind of inference, one he called abduction. Abductive reasoning is the basis for all processes of forming archaeological knowledge. Not much attention has been paid on this topic in archaeology, and all rare cases have been conducted by philosophers, not archaeologists.
The relevance of abductive reasoning in crime scene investigation or Sherlock Holmes type detective work has often been stressed (e.g. Eco and Sebeok 1983). Abductive inference is therefore very important also in archaeology which has been said to resemble the aforementioned sciences very closely (e.g. Klejn 2001: 31, 38-41, 128). The role of abductive reasoning in archaeology has nevertheless been studied very little. Some of the rare exceptions include Leo Klejn’s (2001: 128) view of the abductive nature of archaeological knowledge, Cameron Shelley’s (e.g. Shelley 1996) writings about visual abduction in archaeology and some rare references to abduction as inference to the best explanation that were carried out as part of the processual discourse (e.g. Hanen and Kelley 1995).
All science is, or should ultimately be, based on similar processes of reasoning. According to the later writings of Charles Peirce, abduction can be characterized as a guessing instinct for finding good hypotheses similar to that of the animals’ instinct for doing things that are beneficial or necessary for their survival, that has developed during hundreds of thousands of years of evolution (Paavola 2005: 131-132). To back this up, Peirce argues that it would have been virtually impossible for humans to have developed and reached the current state of knowledge if reasoning was based on mere guessing. In this sense the human mind is, according to Peirce, ‘akin to the truth.’ Abduction is a weak mode of inference that resembles guessing. Abduction is the first phase of inquiry with which ideas and hypotheses are generated. Induction (together with abduction, of course, and to some degree also deduction) are then used to test new ideas and hypotheses. When the basis of knowledge is understood in this fashion, there is little room for arguing in favor of a theory of semantic logic as the grounds and boundaries of knowledge as has been the case traditionally in processual archaeology with its fixation with covering law models and the hypothetic-deductive model.
According to Peirce’s own words, abduction
consists in examining a mass of facts and in allowing these facts to suggest a theory. In this way we gain new ideas; but there is no force in the reasoning. […] induction is, as Aristotle says, the inference of the truth of the major premiss of a syllogism of which the minor premiss is made to be true and the conclusion is found to be true, while abduction is the inference of the truth of the minor premiss of a syllogism of which the major premiss is selected as known already to be true while the conclusion is found to be true. Abduction furnishes all our ideas concerning real things, beyond what are given in perception, but is mere conjecture, without probative force. (CP 8.209.)
Abduction is the process of forming an explanatory hypothesis. It is the only logical operation which introduces any new idea; for induction does nothing but determine a value, and deduction merely evolves the necessary consequences of a pure hypothesis.
Deduction proves that something must be; Induction shows that something actually is operative; Abduction merely suggests that something may be.
Its only justification is that from its suggestion deduction can draw a prediction which can be tested by induction, and that, if we are ever to learn anything or to understand phenomena at all, it must be by abduction that this is to be brought about.
No reason whatsoever can be given for it, as far as I can discover; and it needs no reason, since it merely offers suggestions. (CP 5.171-172.)
Such is the case with much of archaeological knowledge which is often based on very fragmentary evidence of past action. Archaeological knowledge can then only be strengthened with induction, i.e. the occurrence of similar facts in the archaeological record.