The phrase "external expression" is correct and can be used in written English.
It refers to the physical or visible manifestation of something, as opposed to its internal or abstract aspect. You can use "external expression" when discussing emotions, thoughts, or ideas that are being outwardly displayed or communicated through body language, tone of voice, or facial expressions. Example context: During the job interview, the candidate's external expression was calm and confident, but internally, she was feeling anxious and unsure about her qualifications.
But sentences are merely the external expression of judgments, and often they do not express everything one has in mind when judging.
The "external form of the inner character of a human being" (ibid., p. 322) is the ideal of beauty, when the beauty of that external form expresses the goodness of the internal character; correspondingly, the external expression of inner evil is the most hateful form of appearance.
I guess in a way my on/off relationship with drugs was an external expression of my internal struggle.
If everyone isn't clear internally about what you're about, your external expression will be confusing and (worse) actively off-putting.
"The bus company, being an external expression of the system, would naturally suffer, but the basic aim was to refuse to cooperate with evil".
He countered suggestions that it was unrelated to the famous projects by explaining that it shares an external expression of structure.
These are just symptoms; external expressions of a root cause.
All those sorts of games are about allowing people to explore external expressions of their fantasy lives, precisely because the settings are so outlandish.
It insisted (on the authority of a long-standing mystical tradition), however, that theology concerns itself only with the external expressions of this divine source of knowledge.
Only the mystical adepts are in possession of the one true wisdom, the ground of both the external expressions of the divine law and the phenomenal world of human experience and thought.
The variety of symptoms, the internal and external expressions of disease, that result from any disease form the symptom complex, which, together with the accompanying signs, makes up the syndrome of the disease.
