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By Paul Newall (2005)

According to one understanding of the so-called Galileo Affair, the old system of geocentrism was challenged by the new observations made possible by Galileo’s invention of the telescope. In general, it was believed that theories are tested against observations, so that we have a clear demarcation between theoretical and observational statements; the former confirmed or otherwise by the latter.

This picture breaks down quite quickly when we consider it in more depth. To begin with, Galileo's observations were not made via his unaided senses but through a telescope. Some of his contemporaries were extremely skeptical of this instrument; indeed, what Galileo lacked was a theory of optics to explain why those looking through his telescope could trust what they were "seeing" rather than suspecting the apparent celestial phenomena to be tricks of the lenses. Thus what occurred was not the clash of Aristotelian/Ptolemaic theory with observations but instead with Galileo's observations in light of his own optical theories (or lack thereof). We say that the observations were theory-laden.

This line of argument was originally developed in the 1950s and 60s in opposition to the positivist demarcation of observational and theoretical statements, mainly by N.R. Hanson (1958) and later Thomas S. Kuhn (1962) and Paul Feyerabend (in 1981i and 1981ii). It also found a role in critiques of falsificationism. In response it was agreed that some forms of this demarcation failed but that nevertheless there was a natural boundary between statements derived via theoretical considerations and those resulting from the unbiased experience of the world available to us through the senses. In spite of the existence of hallucinations and other sensory phenomena classified as errors (or variously as unscientific, unhealthy or delusional), it was believed that pure impressions could be received by the passive mind and hence constitute direct knowledge of the world. That is, it is possible to identify a normal cognitive process that, although vulnerable to mistakes due to mental illness and other factors, could be relied upon.

A debate took place during the 1980s between Churchland and Fodor (see their 1988 and 1986 respectively for representative instances) concerning the extent to which theory-ladenness plays a part in perception. The latter argued that a distinction should be made between perception and inference, wherein the difficulties discussed above would apply to deriving statements from our observations but not to the actual observations themselves. Churchland and others responded (see his paper A Deeper Unity in Munevar (ed.), 1991, for example) by noting that observation is not simply a matter of perception; instead, it is a cognitive achievement that involves perceiving that something is or is not the case. A number of papers in neuroscience and related areas by Churchland and others have since expanded on this insight, explaining that if our brains held no hypotheses about the world when encountering it (or, alternatively, if these hypotheses were fixed) then we would not be able to learn from new information. This is to say that observations and experiences have to be interpreted to be meaningful and it is this unavoidable involvement of a theoretical dimension – even at the level of brain functioning – that constitutes theory-ladenness. It goes all the way down, as Feyerabend would say.

To return to examples, then, even a straightforward statement such as "this lump of coal weighs one kilogram" is riddled with theory. Whether we include inference from prior experience (i.e. that the heaviness from lifting pieces of coal is conserved over time); the apparatus required to derive weights; the physical theories upon which the instruments and concepts like weight and mass are based; other theories that determine the effect (if any) on weight at different locations; and so on; we are very far indeed from a "basic" proposition.

Not surprisingly, theory-ladenness has been considered a problem because of the importance attached to experiment as an arbiter in testing and/or choosing between physical theories in science. Much discussion has taken place, particularly with regard to the so-called "experimenters’ regress" identified by Collins: the “correct” result of an experiment is one obtained via correctly functioning apparatus; but the latter is nothing more than that which gives a correct result. Similarly, how do we judge the competence of an experimenter other than by whether he or she obtains the "correct" result? For Thomson, the point was that when we talk about repeating an experiment we mean that we "repeat all the features of an experiment which a theory determines are relevant", so we find ourselves "repeat[ing] the experiment as an example of the theory." The apparent lack of any formalised rules (or demarcation criteria, yet again) to decide these issues has led to increased awareness of the importance of other factors, especially sociological ones.

If Churchland is correct about the inevitable role of theory-ladenness, however (insofar as it is what makes learning possible in the first place and our experience of the world genuinely cognitive), then it is not so much a circumstance to be lamented but a realisation that judging what there is or is not in the world by reference to passively observing it was too simplistic a hope to begin with. Lubbock's advice that "what we see depends mostly on what we look for" thus becomes not a cynical refrain but an encouragement to look again and again in different ways as part of a truly reflexive practice.


Selected References:

  • Churchland, P.M., A Deeper Unity: Some Feyerabendian Themes in Neurocomputational Form
  • in Munevar, G. (ed.), Beyond Reason: Essays on Paul Feyerabend (Dordrecht: Kluwer, 1991M.).
  • Churchland, P.M., Matter and Consciousness: A Contemporary Introduction to the Philosophy of Mind (Cambridge, MA: Cambridge University Press, 1988).
  • Feyerabend, P.K., Realism, Rationalism, and Scientific Method: Philosophical Papers, Volume 1 (Cambridge: Cambridge University Press, 1981i).
  • Feyerabend, P.K., Problems of Empiricism: Philosophical Papers, Volume 2 (Cambridge: Cambridge University Press, 1981ii).
  • Fodor, J., Psychosemantics: The Problem of Meaning in the Philosophy of Mind (Cambridge, MA: The MIT Press, 1986).
  • Hanson, N.R., Patterns of Discovery (Cambridge: Cambridge University Press, 1958).
  • Kuhn, T.S., The Structure of Scientific Revolutions (Chicago: University of Chicago Press, 1962).


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