It is not too terribly difficult to spot the signs of an alcoholic. Basically you want to look carefully at the consequences and the lack of control. These are two of the most important criteria when you are watching someone else and trying to gauge their drinking problem.
A true alcoholic gets into trouble. A true alcoholic has problems due to their drinking. They suffer consequences. Now, this does not mean that every alcoholic is going to crash their car, pass out at the bar, and tell off everyone at their family reunion. Those are consequences, yes, but what an alcoholic experiences can be much more minor than this. For example, being late for work, screwing up relationships, getting into yelling matches about their drinking, having their grades slip a notch, staying at a dead end job or not pushing themselves to get a better job, and so on. It does not necessarily have to be the cliche consequences that everyone thinks of, such as drunk driving and so on. Anything that negatively affects a person due to their drinking is a negative consequence, and can be an indicator of sorts.
Now the other issue is the lack of control. Can the alcoholic consistently control their drinking? The word “consistently” is the big key here. Any alcoholic, no matter how messed up, can control their drinking in the short run. Any drunk can maintain composure for a day. Any drunk can hold it down to a few drinks if they really, really have to. But this is the key: at some point, they lose control, and cannot hold themselves back. This is how denial is created. The alcoholic will cling to the memory of when they successfully controlled their drinking, and minimize the times that they lost control.
When you combine these two elements–consequences and a lack of control–then you can begin to really define alcoholism. The alcoholic will continue to return to the bottle (eventually) even in the face of real world consequences. Instead of changing their behavior after suffering consequences due to drinking, they will continue to drink. They might take some time off, but they always return to it. Thus, alcoholism is defined by a pattern, one in which the alcoholic always returns to their drug of choice (alcohol), in spite of the fact that it is no good for them. They will deny the fact that alcohol gets them into trouble and only focus on the times when they drank and experienced no real problems.