Some of the symptoms of alcohol dependence include: increased tolerance, increased usage, withdrawal 12 hours after use, relying on the substance to manage feeling or alter mood, using alcohol even when the consequences are large, acting in ways the person would not do when sober, not being able to recognize the effects or the extent to which alcohol runs choices.
There is evidence that it has a genetic predisposition. Although there is no cure for this disease, but it can be kept in remission by not drinking. If an alcoholic begins to drink again, he/she will return to the previous level of disease quickly and it will likely get worse soon. It is the nature of the disease, not a matter of morals or an issue of intent. some alcoholic drink daily, even large amounts, and keep a job. They may be business owners, lawyers, doctors, teachers, waiters, police officers etc. The family and the alcoholic are affected by the disease anyway. (More about that next time.)
There is a good books on the subject - Understanding the Functional Alcoholic, The Invisible Alcoholic and Drinking, A Love Story, the "big book" Alcoholics Anonymous, to name a few.