Descartes, Meditation  III (first part)

Some technical terminology

Objective reality: The content of a representation (picture, idea, etc.); that is, what the picture, idea, etc. represents.  Example: the content of a picture of Mozart is Mozart himself.

Formal reality: simply the reality of a thing as it is, regardless of what it might represent.  Example: the formal reality of a painting of Mozart is the canvas, oil paint, etc. out of which the painting is made (while the objective reality is Mozart himself).  Things that are not representations of other things (are not ideas, pictures, etc.) have only formal reality.

Efficient cause:  a cause that produces an effect (what we usually call simply “cause”)

Formal cause: a cause that has the same level of reality as its effect (e.g., a cow gives birth to a cow)

Eminent cause: a cause that has a greater level of reality than its effect (e.g., God creates a cow)