Mercury/Neptune combines Mercury's association with thinking, learning, writing and communicating with Neptune's association with dreams, visions, spirituality, idealization, and the imagination:
The Mercury/Neptune combination can be seen in the idealization (Neptune) of the voice (Mercury) in a number of singers, such as Sinead O’Connor, Christina Aguilera, and Amy Lee of the band Evanescence. The lyrics of songs by musicians with this combination often speak of (Mercury) dreams (Neptune), such as in the song “Wildest Dreams” by Taylor Swift, or particularly in the song “Running Down a Dream” by Tom Petty, because of Mercury’s association with the movement of walking and running.
The Mercury/Neptune combination in the chart of Rudolf Steiner is demonstrated in the author’s tendency not only to write (Mercury) on spiritual (Neptune) topics, but also in his ability to communicate (Mercury) spiritual (Neptune) messages (Mercury). “…One must carry the knowledge of the spiritual world within oneself after the fashion of geometry ... [for here] one is permitted to know something which the mind alone, through its own power, experiences. In this feeling I found the justification for the spiritual world that I experienced ... I confirmed for myself by means of geometry the feeling that I must speak of a world 'which is not seen'.”