Lethal damage vs. destruction

The rules of the games often contain nuances that can sometimes be confusing, if one is not aware of them. An example of such nuance is the difference between lethal damage and a destruction effect.

Consider these two questions:

1. There's a Dryad Militant on the battlefield, and someone casts a Searing Spear targeting (and killing) it. Where does the Searing Spear card go?
2. There's a Dryad militant on the battlefield, and someone casts a Doom Blade targeting (and killing) it. Where does the Doom Blade card go?

The Dryad Militant has an ability that says: "If an instant or sorcery card would be put into a graveyard from anywhere, exile it instead." One could easily think that in both cases the instant cards go to the graveyard because Dryad Militant has been killed and therefore is not affecting them anymore. Or perhaps in both cases they are exiled. However, it's not that simple.

The difference between the two cases is subtle, but crucial. The correct answers are:

1. The Searing Spear card is exiled.
2. The Doom Blade card goes to its owner's graveyard.

The reason for this is the difference between destruction and lethal damage (which in itself also causes the creature to be destroyed, but with a delay, as we will see.)

When an effect says that a permanent is destroyed, the destruction happens immediately when that effect is evaluated. There's no waiting for anything, or checking for state-based actions or anything; it's done immediately at that precise moment. Unless the permanent is indestructible or the destruction is somehow prevented (eg. with regeneration) the permanent is immediately put into its owner's graveyard.

When Doom Blade destroys Dryad Militant, the spell is still resolving, and the card is thus still on the stack. The Doom Blade card is put into its owner's graveyard as the last step of resolving the spell, but by that point Dryad Militant is not on the battlefield anymore and therefore it has no effect on the Doom Blade card.

However, when damage is assigned to a creature permanent, that damage doesn't do anything special at that precise moment. It's simply assigned to it (one could think of it as some "damage counters" being added to the permanent.) It's only the next time state-based actions are checked that said damage will destroy the creature (if it's lethal damage.)

State-based actions are not checked until after a spell has completely resolved. This means that Searing Spear will assign the 3 damage to Dryad Militant, which does nothing special to it at this point (other than marking the damage,) and then the Searing Spear card tries to go to the graveyard, but Dryad Militant's ability makes it go to exile instead. Only after that are state-based actions checked, and Dryad Militant is destroyed because of the lethal damage marked on it.

There are other situations that are even more confusing than this, and can sometimes cause confusion even among experienced players. For example, consider this problem:

There's a Tarmogoyf on the battlefield, a creature and a sorcery card in a graveyard (and no other cards), and someone casts Searing Spear targeting the Tarmogoyf. Does it die?

Tarmogoyf's power/toughness are 2/3 before Searing Spear is cast, and the latter deals 3 damage to the creature. So does it die or not?

Many players would say that yes. However, this situation is actually very similar to the one with Dryad Militant above. Like there, the subtlety in this situation is that state-based actions are not checked until after the Searing Spear spell has completely resolved, and putting the Searing Spear card in the graveyard is part of that resolution. Therefore the card is already in a graveyard when the checking is done whether Tarmogoyf is destroyed due to damage or not. At this point there are now 3 types of card in graveyards, and therefore Tarmogoyf is 3/4 and is not destroyed.