Hi Spirit:
Sylvia Browne explains this really well in several of her books. I state this often in responses, because a lot people think ghosts and spirits are the same. They are not... Spirits are those that have moved on, crossed over into the white healing light, and they come back for visits. Ghosts, are those who for some reason, do not cross over into the healing white light, and they are trapped here. By not crossing over, they retain all the emotional and physical characteristics which they had in life and are for the most part, miserable. That's why people see ghosts sometimes with the same injuries they sustained in life, appearance of clothes, etc... With Spirits, it's a little different. A Spirit will never harm you, as they are healed and whole from crossing over. They do visit friends and loved ones on occasion, and when they do... they will apppear in a form that is recognizable to you. They want you to know they are there and who they are and that they are okay. That's another theory about why ghosts and spirits appear as they do.