  A sign has both a reference, and what Frege calls a sense —we can think of the sense as being some kind of embodiment of the mode of presentation. From here on in his paper, sense is under discussion, and modes of presentation fade into the background. A name expresses its sense, and designates its reference. Thus, “morning star” and “evening star” have the same designation, but express different senses, representing different modes of presentation—one is a celestial body last seen in the morning before the sun obscures it, the other is a celestial body first seen in the evening after the sun no longer obscures it. Frege goes on to complicate matters by introducing the idea associated with a sign, which is distinct from its sense and its reference. But the idea is subjective, varying from person to person, while both sense and denotation are said by Frege to be not dependent in this way. Consequently the idea also fades into the background, while sense and reference remain central.