In another thread a while back I brought this up and it wasn't addressed there, so I thought I would give it a thread of its own (apologies if it's been brought up elsewhere):
Another reason to conclude that Isaiah wasn't referring to a divine conception.We also have to remember that this was supposed to be a sign given to the house of Israel. A sign has to be visible. No one of the house of Israel saw Jesus conceived in the womb of Mary, so even if that had happened supernaturally it wouldn't have qualified as a sign.