Internalism and externalism are opposing views of epistemological justification: the question of whether belief in an idea is reasonably supported. In broad strokes, internalism suggests that aspects of the mind—properties of the thinker himself—are inseparable from justification and are ultimately the only reasonable measure of it. Externalism is the belief that reasons independent from the mind not only exist, but are the only ultimately valid justifiers.
In these discussions, justification means something entirely different from the concept of justification in salvation. The philosophical study of “how we know” is called epistemology. Epistemological discussions often divide among three main concepts: truth, belief, and justification. That which is true corresponds to reality. That which is believed may or may not be true. Holding a belief may or may not be justified, independently of whether or not it is true. The main uses of internalism and externalism concern the concept of epistemological justification.
According to internalism, a belief is only justified when a person has some internal sense of that justification. In other words, beliefs are reasonably held only when a person grasps the reasons for his position and is aware of his own thought process. Internalism suggests that a person’s beliefs cannot be justified if the reasons and motivations for the belief have not been considered. Also, this view emphasizes that justified and true have separate philosophical meanings; therefore, if one’s experiences or reasoning is being skewed in some way beyond the person’s control, it does not make those unknowingly biased beliefs unjustified.
According to externalism, the reflective nature of a person’s cognitive process is irrelevant to whether a belief is justified. Externalist justification schemes, such as reliabilism, indicate that, if someone is using reliable methods, his conclusion is justified, even if the person himself knows not whether his process is reliable. In essence, this suggests there will always be some level of ignorance about the justification of our own beliefs, since that which determines justification is outside our own thought processes. This stance can be criticized for making justified all-but-synonymous with true, which short-circuits the reason for considering justification as a separate category.
As purely philosophical concepts, neither internalism nor externalism is explicitly biblical or unbiblical. There are scriptural ideas that suggest an internalist view, indicating that a person’s own thought processes are critical to ethical decisions (Romans 14:5, 23). There are also passages implying that personal approaches can be flawed and that human conclusions are fallible (Proverbs 14:12). Debate over philosophical details such as these is a reflection of their obscurity: there are real-world scenarios that lend weight to both.