Answer

An answer is the opposite of a threat. An answer is a card used to negate a threat. Most instants and sorceries are answers, whereas permanents trend toward being threats, though many enchantments and artifacts are also purely answers.
The old adage is that there are no incorrect threats, but there are incorrect answers; any threat will, unimpeded, end the game, but an incorrect answer will languish and is unlikely to be also a threat to at least contest the opposing threat. Where threats are usually judged by their reliability and clock, answers are judged by their efficiency and flexibility. Answers carry the burden of efficiency more than threats as every turn a threat is unanswered, it accomplishes its controller's game plan, but answering the threat merely contains the situation, so each turn the answer is not castable due to costs puts the answerer behind in both attempting to stabilise the situation and also win the game on their own terms.
Efficiency typically comes down to mana cost, though additional costs should also be weighed. While flexibility does not necessarily need to cost more, design has tended to cost answers that interact with multiple forms of threats at a premium.
In a metagame evolution, the fastest and most linear decks will disregard answers to other decks, as their consistency means other decks are forced to react to them. If this is successful, the next stage generally means more answers and slower gameplans, which ultimately leads to control decks - decks built of answers and card advantage - that disregard any form of proactivity altogether in favor of dismantling others' plans. This is usually answered by another linear deck that is less vulnerable to the standard answers, and the cycle begins anew. 
==Threat reliability==
Threat reliability indicates the degree to which a card has a consistent answer to threats.
The fewer weaknesses a card has, the more reliable it is. If a "new" <c>Savannah Lions</c> was made with "Indestructible" and no differences in cost or function it would be more reliable than the original. Generally cards with built-in weaknesses are not reliable. They can be made so, but alone they are not. Also cards able to "win" the game when they enter the battlefield or a few turns after can be considered reliable. Though it would seem logical to play with 4 cards of any superior reliability-card there are a few cards so reliable that only 1 card is needed in the deck, and usually this is supported by cards that "fetch" that card in one way or another. Cards with effects based on the flip of a coin are probably the most unreliable cards (most of the time they have a 50% chance of failure).
==References==
Category:Magic slang
Category:Magic theory