I have talked to what most people would call dead people. Most of the time, they contacted me -- it wasn't me going off looking to try to find them.
Different people here have said different things; and I think some people are quoting the Bible without understanding it.
The dead know nothing? They base that on:
Ecclesiastes 9:5 For the living know that they shall die: but the dead know not any thing, neither have they any more a reward; for the memory of them is forgotten.
But there are people walking around in living bodies are can also be called dead. As Jesus put it, Let the dead bury the dead.
If the "dead" are not awake spiritually at the point the physical body dies, they will likely go to what some call sheol or hell. They are "dead" spiritually and unaware of what they are, of what spirit is, and of what God is. Thus it is also said:
Psalm 6:5 For in death there is no remembrance of thee: in the grave who shall give thee thanks?
In most cases, it's true that souls in one of the hells (and there are several, I'd say) are so engrossed in by one thing or another, they can perform the same action again and again without taking thought. I would hesitate to describe some of the worst section of hell I have seen.
It is forbidden by my ethical standard to try to contact such souls for the purpose of trying to discern the future or for financial gain and the like. It is certainly okay however to communicate with them for benevolent purposes if there is a chance of helping them. Indeed, when we pray for the dead, angels often go to that section known as Gehinnom or Purgatory to rescue souls.
I don't expect many to believe me; but the book of Jonah says he was in sheol or hell. People can continue to read that to mean he was in a physical fish if they wish; but that's a metaphor. Jonah did remember "God" when he went to sheol.
Jonah 2:2 And said, I cried by reason of mine affliction unto the Lord, and he heard me; out of the belly of hell cried I, and thou heardest my voice.
If there is never any knowing anything in sheol, how could Jonah have invoked the LORD?
I.e. Jonah was not "dead" when he went there. Neither was Jesus when he visited hell and preached. Compare the two. Jesus said we should.
It is perfectly fine for Catholics to talk to the saints. They are not dead! One is not invoking the dead by talking with them. It is not necromancy. I've talked to a few of them myself although I am not a Catholic. Other religions also have "dead" people you can talk to without the least peril -- I have met some of those also. And I've met a few people from the Old Testament. None of these people should be called "dead."
One of my aunts showed up one night. She looked lovely. So beautiful. I said naively, "I thought you were dead." She laughed -- and it was her laugh too -- I've never met anyone who laughed the way she did. She said, "I suppose some people would call it that." Our meeting didn't last long though since there were others about and she didn't want to disturb them.
I have tried to contact "the dead" once or twice. Once was out of idle curiosity, and I got the message back loud and clear that the person wanted to be left alone. She had incarnated again and didn't want to be looking back.
That reminds me when I was a child of about four or five, someone came looking for me. The spirit looking for me was seeing me as "someone else" -- it confused me at the time. For a while, I thought maybe I wasn't my parents' child or something. Later I learned my wife from my past lifetime had gotten someone to try to find me. I had in fact been the person the medium was looking for but I wasn't that person anymore. That wife did visit me at times though after that. She would play tricks at times to get my attention; and that was fine. Once I changed bedrooms with someone living with me; and my "wife" showed up in the bedroom I'd left. It alarmed the woman there.
But believe what you want. You can't know until you see for yourself. I don't expect people to believe me.