How does externalism explain how sensory experience can justify beliefs?

In the context of empiricism, externalism addresses the challenge of how sensory experience justifies beliefs by shifting the focus from an individual's internal awareness to the reliability of the belief-forming process.1

While traditional empiricism struggled to bridge the gap between subjective sensations and knowledge of the external world, externalists—specifically proponents of reliabilism—argue that a belief is justified if it is produced through a reliable process, regardless of whether the individual is consciously aware of that process. Under this framework, humans may be evolutionarily conditioned to respond to sensory stimuli with beliefs about their environment that are generally true and, therefore, justified.1

By defining justification in terms of the reliability of the cognitive or sensory mechanism rather than internal evidence, externalism provides a way to counter skepticism, suggesting that our sensory experiences can indeed serve as a foundation for knowledge even if we cannot introspectively verify the accuracy of every individual sensation.1