What makes a liberal? Good sense and compassion.
Siege
Actually, good sense and compassion hardly describe 'liberal' (I used to be one, I know what I'm talking about). A conservative can have good sense and compassion too, libertarians as well.
Dictionary.com gives this definition for 'liberal':
Favoring proposals for reform, open to new ideas for progress, and tolerant of the ideas and behavior of others; broad-minded.
Now, this is a pretty broad definition too, but it describes what you would call a classical, common-sense liberal, not a person who believes in the political ideology of left-liberalism. Really, this definition could describe libertarians too. No, nowadays when you hear liberal, it generally means left-liberal political ideology.
Common sense and compassion vary among those that purport ANY ideology. Many liberals are idiots and don't even understand their own ideology. This applies to conservatives and libertarians as well. To say common sense and compassion are the only qualities that make a liberal, there would be very few liberals.