The maximum extent of the ice sheets during the Pleistocene period.
In The Foundations of Scientific Inference and in other places throughout his writings, the philosopher of science, Wesley Salmon, provides a narrative about how scientific induction can make sense out of a varying amount of facts to explain the existence of ice sheets across much of North America. In this narrative, it is the scientific capability to make imaginative inferences from the facts to a theory about glaciers that made the human mind capable of coming to the knowledge about about them. jm
Salmon is wrong, though, in his narrative of why we know that glaciers once covered much of North America. As a defender of induction in science, Salmon gives a story about how we can see pieces of evidence that point to the events of the Ice Ages and that from those pieces of evidence, our confidence becomes greater that a continental ice sheet once extended as far as Illinois. This all fits within his probabilistic explanation of induction and within his thought, it certainly makes sense how more evidence of that event would increase the scientific robustness of a theory. However, that does not change that Salmon fundamentally got the process backwards.
Physical objects in the world did not explain themselves to us and people did not gather all of the evidence of the extent of the Laurentide ice sheet and then come to create a theory about Ice Ages from them. Instead, what happened is that the human idea that there was such a thing as Ice Ages came to guide scientists into finding more evidence to corroborate that theory. Facts did not lead to theory; rather theory led to facts.
There are simply no such things as physical entities independent of the ideas held by people that can be labeled “facts.” Indeed, the common-place notion that there are such entities in the world and that all someone has to do to discover the truth is to gather all of these “facts” completely misconstrues the process by which human knowledge grows. That human beings can even look at the world and say there are such things as facts is a product of them holding theories that allow them to categorize the world in such a way as to be able to point towards otherwise epistemologically inert objects and to say that they are “facts.” Thus facts occupy World Two of Karl Popper’s ontology: facts only exist where the mind interacts with the physical world and classifies it according to purely mental objects (i.e. theories) that exist independent of the physical world*.
Thus that we are able to see evidence everywhere we look that point towards the existence of the Laurentide ice sheet cannot be understood as simply facts guiding the mind towards adopting a theory. Rather, we are able to see all of that evidence because the human mind holds a certain theory and that theory makes possible the mind to see those physical objects as pointing towards the existence of primordial ice sheets tens of thousands of years ago.
Facts independent of theory thus don’t exist. All that exist are physical objects that fit well into the classification schemes of theories and some theories that have classification schemes that can be seen as better capturing the real phenomena of the world. Some classification schemes prove to be very capable at predicting how future events can be classified, at which point we can say that they have proved their mettle. And other schemes prove to be incapable of predicting how future events can be classified, at which point we can say that they have been classified. As a result, science is not fitting theories to facts; rather it is the competition of many different systems of classification that bring along with them different understandings of the physical objects out in the world.
* “In this pluralistic philosophy consists of at least three ontological worlds: the first is the physical world or the world of physical states; the second is the mental world or the world of mental states; and the third is the world of intelligibles, or of ideas in the objective sense; it is the world of possible objects of thought: the world of theories in themselves, and their logical relations; of arguments in themselves and their logical relations; and of problem situations in themselves.” - Karl Popper in “On the Theory of Objective Mind” as published in Objective Knowledge (Oxford: Oxford University Press, 1979), pg. 154.
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