Why, a dog, whenever he sees a stranger, is angry; when an acquaintance, he welcomes him, although the one has never done him any harm, nor the other any good.
 Plato, The Republic. copy citation

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Author Plato
Source The Republic
Topic welcome strangers
Date
Language English
Reference
Note Translated by Benjamin Jowett
Weblink http://www.gutenberg.org/files/1497/1497-h/1497-h.htm

Context

“Would not he who is fitted to be a guardian, besides the spirited nature, need to have the qualities of a philosopher? I do not apprehend your meaning. The trait of which I am speaking, I replied, may be also seen in the dog, and is remarkable in the animal. What trait? Why, a dog, whenever he sees a stranger, is angry; when an acquaintance, he welcomes him, although the one has never done him any harm, nor the other any good. Did this never strike you as curious? The matter never struck me before; but I quite recognise the truth of your remark. And surely this instinct of the dog is very charming;—your dog is a true philosopher.” source