Here therefore we have three things to explain, viz.

First, The original impression.
Secondly, The transition to the idea of the connected cause or effect.
Thirdly, The nature and qualities of that idea.
As to those impressions, which arise from the senses, their ultimate cause is, in my opinion, perfectly inexplicable by human reason, and it will always be impossible to decide with certainty, whether they arise immediately from the object, or are produced by the creative power of the mind, or are derived from the author of our being.

Nor is such a question any way material to our present purpose.

We may draw inferences from the coherence of our perceptions, whether they be true or false; whether they represent nature justly, or be mere illusions of the senses.
When we search for the characteristic, which distinguishes the memory from the imagination, we must immediately perceive, that it cannot lie in the simple ideas it presents to us; since both these faculties borrow their simple ideas from the impressions, and can never go beyond these original perceptions.

These faculties are as little distinguished from each other by the arrangement of their complex ideas.