You have no idea how often this question is asked. Grieving is hard enough, but if we know that those who have died are able to watch over us, it
For example, naysayers argue that it's all a figment of the imagination. Or they might argue that what is present is your "Dad-in-you" -- that is, a sense of your Dad that you have internalized. A counterargument might be: So what? Whether the felt presence of a deceased beloved is imagined or "real," does it really matter? If someone's presence provides comfort and solace, isn't that good enough?
If you are one who needs concrete evidence of something before you can believe it, you may struggle to believe in your Dad's presence. On the other hand, if you really want to feel his presence, you might find yourself willing to suspend any disbelief, or not be swayed by those who argue vehemently against it.
Know that this is a theme that shows up in the lives of many who are grieving. There are some uncanny stories that don't necessarily provide proof, but certainly raise a sense of possibility that contact with the deceased is in some way possible.
If you would like to read more on this topic, I recommend starting with Blessings From the Other Side: Wisdom and Comfort From the Afterlife for This Life by Sylvia Browne and Lindsay Harrison. Movies that have addressed this topic include: Contact, Ghost Town, The Sixth Sense and Ghost. Rent one or two of them -- and take heart in your own conclusion.
sure does ease the pain. The problem, to some people, is that there is no way of proving, without a doubt, the presence of the deceased.