Final answer:
The main objections to the Externalist's Response to Scepticism are that it does not require subjects to be aware of the reliability of the external factors justifying their belief, potentially leaving room for skepticism, and it does not align with the common sense approach evoked by philosophers like G. E. Moore, which is based on immediate sensory evidence.
Step-by-step explanation:
The objections to the Externalist's Response to Scepticism revolve around the debate between externalism and internalism in the justification of beliefs. Externalists argue that factors outside the individual's mental state can contribute to the justification of a belief. For example, Alvin Goldman suggests that beliefs are justified if they are produced by reliable belief-forming processes, which is an externalist standpoint. A key objection to this approach is that it does not require the subject to be aware of these external factors, arguably leaving room for skepticism since the subject cannot ascertain the reliability of the justification for themselves.
On the other hand, internalists advocate that justification must rely on evidence accessible to the believer's consciousness, effectively addressing the skeptic's demand for certainty from the internal perspective of the believer. Critics of externalism may argue that it fails to provide a satisfactory defense against skepticism, because if the justification of a belief is external to the subject, then the skeptic could argue that the subject does not actually know that these external factors are reliable. They could still be, for instance, a 'brain in a vat,' mistaken about their cognitive processes.
Moreover, objections may arise from the perspective of common sense, as demonstrated by G. E. Moore's response to skepticism, which relies on intuitive and immediate sensory perceptions. Critics of externalism might suggest that Moore's commonsensical approach highlights the intuitive lack of conviction in an externalist's impersonal, external justification, suggesting that it fails to fully overcome philosophical skepticism.