Any object whose attributes, i.e. all that may truly be predicated, or asserted, of it, will, and always would, remain exactly what they are, unchanged, though you or I or any man or men should think or should have thought as variously as you please, I term external, in contradistinction to mental. [—]

The main difference between the external, as I use the term, and the real, as I employ that term, seems to be that the question whether anything is external or not is the question of what a word or other symbol or concept (for thinking proper is always conducted in general signs of some sort) is, I say, a question of what a symbol signifies; while the question of whether anything is real or is a figment is the question what a word or other symbol or concept denotes.