Is Christian Shephard (Jack's Dad) a ghost or does he have actual corporeal form on the island?

Agreed I believe Christian is alive and real and not just an apparition although that being said in the past he has seemed to appear and disappear in inexplicable ways. But I think he was resurrected because the of the island the way Locke was recently brought back from the dead.

This has always confused me,but my guess is that there are two Christians - one that Jack sees when he's going crazy (in white shoes, just like he burried him in) and one that's been "resurrected" or something (in black shoes).

I think that the White Shoed Christian is actually the Smoke Monster taking over Christian's body to mess with Jack, just like I think it did with Yemi to mess with Eko.

I was confused until Locke returned to the island alive. This made me think Jack's dad is alive as well. If this in deed is the case, when he returns to the regular world, will he be dead? The same goes for Locke, is this the only way Locke will be alive? I amor this show, so many questions, so little answers!

Christian's death, though not shown on-screen, has been confirmed in a Official lost podcast (April 20, 2007 Edition). Even further clarification was received in "Access: Granted", when Carlton Cuse stated "In terms of actually physically corporeally in existence... he's dead".

He is, along with Locke and Yemi, one of three previously deceased bodies that later appeared to be living people. What's interesting to note is that all three of these men were already dead, and on airplanes, before they came to the Island. A few of Yemi's appearances were confirmed to be influenced por the Monster in the Official lost Podcast (March 21, 2008 Edition), however, Christian was confirmed as being one of three characters (Yemi and Kate's horse being the other two) to be classified as "undead".

The smoke monster (later revealed to take the form of John locke )
Took the form of Christians body so Jack would follow him and find water.