Constant conjunction

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Constant conjunction: Repeated observation of events of type A being followed by events of type B is called the constant conjunction of A and B. The critical philosophical question is whether observation of constant conjunctions of this type allows us to conclude that event A causes event B. To understand the issue, which is of central importance in philosophy of science, it is helpful to look at a few examples. According to a Wall Street Journal article, Juneau County in Wisconsin has voted for the Presidential winner in every election since 1980. Thus we have a constant conjunction - win of popular vote in Juneau County is followed by win of presidential election. But, it should be clear that this is not a causal relationship. On the other hand, every time we light a match and throw it onto a bundle of dry cotton, we will see that the cotton burns. This is a causal relationship -- we expect this sequence of events to hold all the time. It seems intuitively clear that we can distinguish between causation and correlation, and scientific laws depend on causal relationships. However, the question of how we can differentiate between the two types is the subject of great controversy and debate. David Hume argued that causation is just constant conjunction - after observing events of type A being followed by those of type B over a long period of time, we become convinced that A causes B. But this is a deeply problematic position. For example, if we observe sunrise follows crowing by a rooster for a long period of time, would we believe that crowing causes sunrise? Immanul Kant was motivated to develop his philosophy by this argument, which he considers as an attack on science by Hume -- see "Kant and Hume on Causality" in the Stanford Encyclopedia of Philosophy (SEP). After all, if the law of gravity is just a sequence of observations (of apples falling to the ground) in the past, there is no guarantee that the same relationship will hold in the future (apples might begin to shoot up in the air instead). The SEP article notes that there is no consensus on exactly what Kant proposes as a solution to the problem -- how can we learn about causal relationships and differentiate them from accidental correlations. Similarly, there is no consensus on whether or not Kant was successful in resolving this problem.

Overview[]

The philosopher David Hume used the phrase frequently in his discussion of the limits of empiricism to explain our ideas of causation and inference. In An Enquiry concerning Human Understanding and A Treatise of Human Nature Hume proposed that the origin of our knowledge of necessary connections arises out of observation of the constant conjunction of certain impressions across many instances. There is considerable controversy over exactly what is the position of Hume; for a clear discussion of many different alternative interpretations of Hume, see "David Hume: Causation". A more modern conception would argue that scientific law is distinguishable from a principle that arises merely accidentally because of the constant conjunction of one thing and another, but there is considerable controversy over what this distinguishing feature might be.

Although British empiricism and associationist philosophers elaborated on Hume's fundamental idea in many diverse ways, and metaphysicians like Immanuel Kant tried to dissipate the position,^{[verification needed]} the force of his arguments has remained remarkably robust, and they have found unexpected support in three scientific discoveries of the 20th century: Ivan Pavlov's laws of conditioning; Hebbian neural networks; and spike-timing-dependent plasticity (STDP).

In Pavlov's framework, an unconditioned stimulus can follow in constant conjunction a conditioning/conditioned stimulus within a timeframe of milliseconds to several seconds, and result in the conditioned stimulus having many of the properties of the unconditioned stimulus. Donald Hebb explained this as an intrinsic property of cell assemblies within the nervous system to form connections within large cliques of cells whenever those cells fire together within a reasonably short period of time. (A modern shorthand for his ideas states: "Cells that fire together, wire together".) Modern neuroscience has confirmed this insight as a product of the activity of synapses and STDP, so structured to strengthen connections between cells that fire within very short periods (10s of milliseconds) of each other. The longer time periods of classical conditioning are presumably a large-number effect of cliques of these synapses and cells.