User blog comment:Rollnstoned/Types of Supports/@comment-1330314-20130812143115/@comment-1330314-20130812213201

That's not actually the case:
 * may have a heal, but he's primarily a tank. He doesn't have a poke, and when building tanky doesn't deal enormous amounts of damage, and despite his heal benefits his team primarily by initiating and tanking, not by sticking to the ADC.
 * , similarly, doesn't deal enormous amounts of damage by herself, and her poke is inefficient when used alone. All of her abilities are meant to be used on or for the carry, so she's a defensive support.
 * and both have a shield, but that's their only defensive capability. Their effectiveness comes from CCing and debuffing enemies, so they count as offensive casters. If you stick to the carry as either one of them you'd only be using one ability out of their entire kit.