A logical argument is one that relies on the principles of classical logic to establish veracity. An excellent example is this classic: If A = B and B = C, then A = C. We can replace these placeholders with any number of options. For instance: Dogs are canines, canines are mammals, therefore all dogs are mammals.
Each proposition, or statement, in this example follows a logical order, the hallmark of a logical argument. If we removed the middle proposition (canines are mammals), the argument would be: Dogs are canines, all dogs are mammals. While we might know this is true, the missing proposition means the argument is no longer presented logically.