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Webster 1913 Edition

Noun.

The quality of being manifest to the senses; external acts or appearances; regard for externals.

This

externalism

gave Catholicism a great advantage on all sides.

E. Eggleston.

(Metaph.)

That philosophy or doctrine which recognizes or deals only with externals, or objects of sense perception; positivism; phenomenalism.

externalism ‎(plural externalisms)

Excessive regard to outward acts or appearances, especially in religion. The denial of internalism.
The act of judging by outward appearance or acts.
The belief that only things that can be observed by senses are real.