I recently read an old thread from February on this site in which an active member of the blogging community made questionable claims regarding the definition of card advantage, and that prompted me to write this piece. I hope it's helpful and informative to those who feel they don't fully grasp some of the game's more intricate concepts.
For as long as I can remember, I've been a huge fan of control decks. It's pretty funny and strange for me, as I never really got into casual magic, and as the very first archetypes I played were Affinity and Tooth and Nail, it took me awhile to figure out where my blue mage roots came from. Then it hit me.
Drawing cards is awesome!
Everyone knows this, and everyone pretty much agrees that if the price is right, drawing cards is probably the most impactful thing you can do in magic besides putting your opponent from 1 to 0 (die in a fire, Platinum Angel). Control decks are often designed to gain an incremental advantage over the course of the slow game by doing things such as, you guessed it, drawing cards.
Drawing cards is very commonly labeled 'Card Advantage' which, to be aptly put, means that the player with more cards probably has the advantage. Therefore, cards that draw cards are awesome and have a deeper impact on the game than card that reads "destroy target creature".
However, it seems that people don't fully grasp the concept of card advantage, because drawing cards is only one aspect of the full array of advantage you can gain. Bear with me, as I'm just going make up labels as I go:
The major types of card advantage are Card Draw, Discard, X for Y Sweeps, and Virtual. I hope to explain each type individually so that players might better understand the roles of cards that produce advantage, and give examplets of each type.
Card Draw
Card Draw is basically what we have been talking about. Cards that trade themselves for more cards are producing card advantage. Tidings is a great example of a simple card that produces card advantage. Controlish archetypes often rely on card drawing spells to help them gain advantage. Most control decks play spot removal, which is one of your spells used to take out one of their creatures; no advantage is gained. The card draw keeps those removal spells coming, and eventually yeild a late game threat that the opponent cannot overcome. Also, cards like Dismiss are considered card drawing advantage because you are trading with the opponent's spell then calculating the draw you get as an addition, putting you up one card.
Discard
Discard is more often than not proactive disrupting card selection, ie trading one of your cards for one of theirs. However, some discard spells are incredibly powerful forms of card advantage, namely Persecute, which used to be UR Magnivore's worst nightmare several years ago. A persecute against a monocolored deck can yeild drastic card advantage. Jon Finkel made his opponent, Chris Benafel, discard 6 cards from his hand in the finals of Nationals 2000, which essentially put Benafel much too far behind to win at that point. Jon played one spell, and Benafel was forced to bin 6 cards. That trade allowed Jon to easily win the match, and put him on his way to being the only magic player in history to win the National Championship, Team World Championship, and individual World Championship trophies in the same year.
X for Y Sweeps/Trade
Sweeps, more commonly referred to as WoG Effects, are basically onboard trades you can make in which you trade one card for multiples of the opponents cards. Obvious, basic cards include the namesake Wrath of God and Damnation, Pyroclasm, Hurricane, etc. However, when applying this definition, there are instances where cards like Seige Gang Commander have the same effect. If my opponent were to have three Pestermites on the board, I could sack my goblins to kill each faerie. Those cards are real, while my goblins are just tokens. In this situation, I'm still generating card advantage. Another example still is where the player can generate advantage through trading advantageously in combat.
Virtual
Virtual card advantage is somewhat harder to grasp as a concept, because no actual trades are being made in the literal sense. Virtual Card Advantage is any scenario in which you can blank multiples of your opponents cards. An awesome example of this comes from an FNM I participated in back in February. My opponent has 5 red creatures on his side of the board and one card in hand. Facing eminent doom, I untap and rip Teferi's Moat off the top of my deck. I cast it naming Red, and now all of a sudden, I've just gained card advantage because his creatures are no longer able to function properly (aka bash my face in). Sometimes, Virtual card advantage does have to even involve you making a play. If I'm playing a monoblack aggro deck, and my opponent has four terror and four dark banashing, I've blanked a total of eight cards in his deck before the game began without actually doing anything.
Card Selection
Before we go, there's one more thing I'd like to discuss, regarding Card Selection. In Magic, there are many cards that tell you to draw cards, but don't actually generate card advantage. For example, if I cast Careful Consideration in my main phase, I will draw four, then discard two. The card advantage count right there is x-y-z=n, where x equals the draw, y equals the card you played, and z equals the discard. Therefore, n, your total generated advantage, is +1. However, if you cast the consideration at instant speed, it no longer generates advantage because you have to discard an additional card, which makes n equal 0. This is called card selection.
Basically, card selection is when a card you cast replaces itself with another card, but does not actually generate card advantage. Examples of Card Selection include Telling Time, Impulse, Brainstorm, and Ponder. The Scry keyword from the Mirroding Block is a classic example of card selection. The thing about card selection is that people sometimes see things like 'Careful Study: draw 2 cards, discard 2' and immediately think card advantage! Careful study is actually card disadvantage, as it puts you at n = -1. However, it is still card selection.
I hope this analysis of card advantage has been helpful. If I get un-lazy, I may pick up the pen again soon.