88. So long as we attribute a real existence to unthinking things, distinct from their being perceived, it is not only impossible for us to know with evidence the nature of any real unthinking being, but even that it exists. Hence it is that we see philosophers distrust their senses, and doubt of the existence of heaven and earth, of everything they see or feel, even of their own bodies. And after all their labouring and struggle of thought, they are forced to own we cannot attain to any self-evident or demonstrative knowledge of the existence of sensible things(669). But, all this doubtfulness, which so bewilders and confounds the mind and makes philosophy ridiculous in the eyes of the world, vanishes if we annex a meaning to our words, and do not amuse ourselves with the terms _absolute_, _external_, _exist_, and such like, signifying we know not what. I can as well doubt of my own being as of the being of those things which I actually perceive by sense: it being a manifest contradiction that any sensible object should be immediately perceived by sight or touch, and at the same time have no existence in nature; since the very existence of an _unthinking being_ consists in _being perceived_. 89. Nothing seems of more importance towards erecting a firm system of sound and real knowledge, which may be proof against the assaults of Scepticism, than to lay the beginning in a distinct explication of _what is meant_ by _thing_, _reality_, _existence_; for in vain shall we dispute concerning the real existence of things, or pretend to any knowledge thereof, so long as we have not fixed the meaning of those words. _Thing_ or _being_ is the most general name of all: it comprehends under it two kinds, entirely distinct and heterogeneous, and which have nothing common but the name, viz. _spirits_ and _ideas_. The former are active, indivisible, [(670)incorruptible] substances: the latter are inert, fleeting, [(671)perishable passions,] or dependent beings; which subsist not by themselves(672), but are supported by, or exist in, minds or spiritual substances. [(673)We comprehend our own existence by inward feeling or reflection, and that of other spirits by reason(674). We may be said to have some knowledge or _notion_(675) of our own minds, of spirits and active beings; whereof in a strict sense we have not _ideas_. In like manner, we know and have a _notion_ of relations between things or ideas; which relations are distinct from the ideas or things related, inasmuch as the latter may be perceived by us without our perceiving the former. To me it seems that _ideas_, _spirits_, and _relations_ are all in their respective kinds the object of human knowledge and subject of discourse; and that the term _idea_ would be improperly extended to signify _everything_ we know or have any notion of(676).]