Question: "What is coherentism / contextualism? What is foundationalism?"
Answer: Coherentism (or contextualism) and foundationalism are opposing approaches to determining if a certain belief is warranted. In general philosophy, this analysis is referred to as justification, which is entirely separate from the biblical concept of justification as related to salvation. Philosophical justification deals with whether a person has an acceptable confidence in some belief. Foundationalism takes an approach that is more objective but also more abstract. Coherentism is more practical but suffers from logical weaknesses.
Philosophical discussions of knowledge, or epistemology, broadly divide into three independent ideas: a statement may be true or false; a person may accept that statement or reject it; and that opinion may be supportable or unreasonable. These three concepts, respectively, are “truth,” “belief,” and “justification.” These are truly independent: a person can believe something true for irrational reasons, or he can (according to some views) reasonably believe something that turns out to be false.
Ideas such as coherentism and foundationalism are differing views of justification. Rather than dealing directly with what is true or false, these views seek to define what makes a belief justified: at what point is it reasonable to assume some belief is true?
This distinction is especially relevant because there is a “coherence theory of truth,” which is not the same thing as coherentism or contextualism with respect to justification. When comparing foundationalism and coherentism, we must remember that these are not discussions of what is actually true but varied opinions on what makes a belief justified, or reasonable for a person to hold.
Foundationalism can be visualized as a tree or a pyramid or a brick wall. To be justified, a belief needs to be supported by some other belief, which is itself justified, and so on until the ultimate basis for those beliefs, the foundation, is reached. According to foundationalism, all justified beliefs are ultimately grounded in certain other beliefs that cannot be derived from or verified by other beliefs. These axioms are foundational and necessary. They “must be believed” in order to have any knowledge at all. In order for a belief to be properly justified, foundationalism demands that it be traced to one or more of these fundamental maxims.
Coherentism (contextualism) can be visualized as a massively complex web or a cloud or a tangle of cords. To be justified, a belief must be supported by other beliefs. The more contact the belief has with other ideas—the more it coheres with the surrounding structure—the more justified it is. Like looking at a cobweb from the center out, there might not be a perceivable end point. Connections may branch off in many directions without having any self-anchored end point. According to coherentism, justified beliefs are those that have “good enough” support from other beliefs, and they do not require the chain of support to be verified until it stops—if it ever does. For a belief to be properly justified, coherentism demands it be connected to a subjectively sufficient number of supporting beliefs.
Foundationalism is supported primarily by force of logic. The existence of foundational truths is demonstrated in the theories of basic mathematics, such as “a number is equal to itself.” That statement can’t be deduced from other ideas, but neither can it be denied without obliterating logic and mathematics themselves. Foundationalism allows the strongest possible ties between truth and belief by creating a direct link between the two. It also avoids the problem of an argument eventually being used to support itself. However, foundationalism is also abstract. While it might be logically possible to trace all facts and ideas to basic maxims, it is not practical to do so, and such tracing is virtually never done in the real world.
Coherentism’s main advantage is practicality. Tracing a belief all the way to fundamental axioms is beyond most people, even if they were inclined to pursue such a discovery. It’s also true that, in some cases, the chain of justification becomes unclear: not all steps in the process are simple and easy to determine. That means most people in the real world approach justification through a practical form of coherentism, even if they believe there “ought to be” an objective end point for their reasoning. The danger is that coherentism easily becomes relativism. It can even lead to solipsism, since what constitutes a “good enough” connection is deeply subjective.
Ultimately, both foundationalism and coherentism can be consistent with a biblical worldview. This is because neither is a statement about what “is true” or what one “should believe,” but only the process by which one determines if there is a justified link between a belief and truth (see 1 John 4:1; 2 Corinthians 13:5; Acts 17:11). While foundationalism seems more robust, human fallibility must be taken into account, leaving room for coherentism in some applications.