Dr. Ellis discusses how addiction excels at keeping people around it off balance and in doubt. He then describes 4 common signs of addiction that should help you decide if you need to take action.
Several tools help to quantify the problem relationship with alcohol. The first is from the book mental health professionals use to diagnose psychiatric and psychological disease, which is called:
As the concerned person you can answer the questions in terms of "have you seen" the behavior described in the questions.
In their book Love First, Jeff and Debra Day have five other self-quizzes that deal with special circumstances such as teens and the elderly. (see pp. 289 ff)
Depending on the willingness of the suspected alcoholic/addict you can use these tools for discussion. A healthy discussion, however, is somewhat unlikely due to his or her irrational defenses.