These latter perceptions are all so clear and evident, that they admit of no controversy; though many of our ideas are so obscure, that it is almost impossible even for the mind, which forms them, to tell exactly their nature and composition.

Let us apply this principle, in order to discover farther the nature of our ideas of space and time.
Upon opening my eyes, and turning them to the surrounding objects, I perceive many visible bodies; and upon shutting them again, and considering the distance betwixt these bodies, I acquire the idea of extension.

As every idea is derived from some impression, which is exactly similar to it, the impressions similar to this idea of extension, must either be some sensations derived from the sight, or some internal impressions arising from these sensations.
Our internal impressions are our passions, emotions, desires and aversions; none of which, I believe, will ever be asserted to be the model, from which the idea of space is derived.

There remains therefore nothing but the senses, which can convey to us this original impression.
Now what impression do oar senses here convey to us?
This is the principal question, and decides without appeal concerning the nature of the idea.
The table before me is alone sufficient by its view to give me the idea of extension.

This idea, then, is borrowed from, and represents some impression, which this moment appears to the senses.