Philosophical discussions generally consist of productive debate in which two or more people attempt to rationally argue for different sides of a question. They each try to think up and explain a logical argument in support of their position while constructively trying to offer logical rebuttals of the other person's position. Though called arguments, the philosophers generally have a lot of respect for each other and enjoy having the discussion in a friendly tone. In fact, it becomes very difficult to have a worthwhile philosophical discussion without a lot of respectfulness and friendliness. 

Unfortunately, sometimes one person may use an ad hominem argument. An ad hominem argument consists of replying to a person's argument by merely attacking the character of the person making the argument. An ad hominem argument is also called a personal attack or an irrelevant insult. For example, if Joe claims that the sky is blue, Bob would be making an ad hominem argument if he responded by saying, "No, it isn't because you are an ugly moron." 

An ad hominem is a fallacy, and it is illogical. Worse yet, it may cause the discussion to break down into an unproductive name-calling contest.