A person who drinks a half a fifth of hard liquor (daily, 5 yrs.) is trying to convince others that he can just stop on his own.this possible at all?

It would : Be best he does this with the help if medical professionals. It would be very dangerous to go. "Cold turkey". Drinking that amount if liqueur. The withdrawal symptoms are potentially life threatening and should be monitored in medical environment. If he truly want to stop. Get him in with a good rehab facility. It would help both medically and emotionally

Yes, but not likely: Anything is possible. People drink for all sorts of reasons and stop drinking only when they are truly ready to change. Even with help, a person will not stop drinking if they do not want to stop. From a medical standpoint a person who has been consuming large quantities of alcohol and suddenly stops drinking may experience withdrawal symptoms ranging from none to death. Many factors involved.