On Sense and Reference

“The reference and the sense of a sign are to be distinguished from the associated idea. If the reference of the sign is an object perceivable by the senses, my idea of it is an internal image, arising from memories of sense impressions which I have had and acts, both external and internal, which I have performed. Such an idea is often saturated with feeling; the clarity of its separate parts varies and oscillates. The same sense is not always connected, even in the same man, with the same idea. The idea is subjective; one man’s idea is not that of another.”

- Gottlob Frege