Presuppositionalism vs evidentialism

These two terms that I had never heard before came up when listening to some Christian apologetic podcasts (specifically Please Convince Me and Stand to Reason). There seems to be some split between Christian apologists on these two approaches to apology. What is interesting is that the normal course of science uses both, so there really shouldn’t be any split for any rational approach to justification of the ideas. Evidentialists argue for the exists of the Christian God through outlining of the evidence of the Christian God, and then follow the logical arguments that come from that. Presuppositionalists seem to assume the existence of the Christian God, but then try demonstrate that the world only makes sense if you do so.

In other words, they are “X is true and here is the evidence or logical argument for X” and “if we assume X, then W, Y, and Z that we observe make sense…otherwise W, Y, and Z do not make sense”. Both of these are done in science all the time. Take, Newton’s law of gravitation for example. When he proposed the form of the gravitational force, {F \sim 1/r^2}, Newton did not provide direct evidence for this form…that was first done only 100 years later by Cavendish. What he did is say was “if the form of the force is {F \sim 1/r^2}, then many other things make sense (i.e. motion of the planets, the tides, the falling of objects near the surface of the Earth, etc…)”. In a way, this is a presuppositionalist argument: if we take X to be true, then our observations of W, Y, and Z make sense. This type of argument is considered evidence in science, and is done all the time. Really, the two ways that scientific theories can be justified are:

  1. directly test the assumptions of the theory
  2. spin out the consequences, and compare with observation

The former is, what the apologists would call, evidentialist while the latter is presuppositionalist. In a fit of irony, I have heard many so-called refutations of atheists on the topic of morality of the form “atheists claim there is no objective morality, so they can’t even state that the actions of the God in the Old Testament are evil”. However, all these atheists are doing are using a preuppositionalist argument: “If we assume that God is good, and that the ‘good’ is defined by the statements of Jesus and the ten commandments, then we can demonstrate that the other acts of God in the Bible are evil.”

Personally, I just like to lump both terms into “rational argument” and leave it at that. They do little to shed light on the issues, and to me they are a distinction without a difference.


About brianblais

I am a professor of Science and Technology at Bryant University in Smithfield, RI, and a research professor in the Institute for Brain and Neural Systems, Brown University. My research is in computational neuroscience and statistics. I teach physics, meteorology, astonomy, theoretical neuroscience, systems dynamics, artificial intelligence and robotics. My book, "Theory of Cortical Plasticity" (World Scientific, 2004), details a theory of learning and memory in the cortex, and presents the consequences and predictions of the theory. I am an avid python enthusiast, and a Bayesian (a la E. T. Jaynes), and love music.
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