The "then" Gate: Wording Decides Whether the Follow-up Happens

Many effects are written as "do X, then Y." In PSCT, "then" means Y happens only if X was successfully performed. But how strict that gate is depends entirely on how X is worded. Judges must read X's exact wording before deciding whether Y applies — do not assume "then" always requires everything to succeed, and do not assume it always proceeds.

"destroy as many … as possible, then Y" — lenient gate

When X is phrased as "destroy as many monsters as possible" (or similar maximal-effort wording), Y applies as long as at least one card was actually destroyed. A partial result is fine.

• 3 opponent monsters, 1 protected from destruction → 2 are destroyed → Y applies.
• Every relevant monster is protected/unaffected → zero destroyed → Y is skipped.

"destroy that card / those targets, then Y" — strict gate

When X names specific card(s) — "destroy that card," "destroy those targets," "destroy both those targets" — Y applies only if those named targets were actually destroyed. If a named target survives (protection, leaves the field first, etc.), the gate for Y is not met for that target.

How protection interacts

A continuous "cannot be destroyed by your opponent's card effects" effect (for example, one granted by Lingering Effects Granted by Summon Material) prevents the required destruction. Under either wording above, preventing the destruction can break the "then" gate and stop Y.

Worked example — Illusion Gate

Illusion Gate — "Pay half your LP; destroy as many monsters your opponent controls as possible, then you can Special Summon 1 monster from your opponent's GY to your field, ignoring its Summoning conditions. You can only apply this effect of 'Illusion Gate' once per Duel."

"My opponent activates Illusion Gate while I control only one monster, which cannot be destroyed by their card effects. Can they Special Summon from my GY?"

— Answer: No. "Destroy as many as possible" destroys zero here, because the only monster is protected. The Special Summon is a "then" follow-up that requires at least 1 monster to have been destroyed, so it does not apply. If the opponent had also controlled an unprotected monster, that one would be destroyed (≥1 destroyed), the gate would be satisfied, and the Special Summon would proceed.

See also Chain Resolution — Step by Step and Properly Summoned and Extra-Deck Sends. Note that Illusion Gate's "ignoring its Summoning conditions" clause is a separate allowance (it bypasses the properly-Summoned check); it does not remove the destruction gate.

"do X, then you can Y" where X is mandatory — X must be possible or Y is lost

The same gate decides whether a monster's self-revival happens. When a "If this card is Tributed/sent" effect reads "add 1 [card] … , then you can Special Summon this card," the add is X and the Special Summon is the "then" follow-up Y. If anything makes the add impossible at resolution — a floodgate like Droll & Lock Bird (no adding from the Deck to the hand), Ash Blossom & Joyous Spring negating the add, or simply no valid card left to add — then X fails and Y (the Special Summon) does not happen.

Ame no Habakiri no Mitsurugi / Ame no Murakumo no Mitsurugi — "If this card is Tributed: You can add 1 'Mitsurugi' card from your Deck to your hand …, then you can Special Summon this card."

"Can the 'Mitsurugi' Ritual Monster still Special Summon itself back after Tributing itself if I can't use the add from Deck because of Droll & Lock Bird?"

— Answer: No. The add is the first part of the effect; the self-Summon is a "then you can" follow-up gated on the add. With Droll & Lock Bird preventing the add from the Deck, the add fails, so the Special Summon is lost — exactly the same reason it can't come back with no valid "Mitsurugi" to add, or if Ash Blossom negates the add. (Note the whole effect opening "You can" makes it optional to start, but once you choose to use it, the "then" still requires the add to succeed.)

The same applies at activation for an effect whose required first action already has no legal application. If an effect says "You can Set 1 [theme] Spell/Trap from your Deck, then you can destroy 1 monster," it cannot be activated with no legal Set available merely to reach the optional destruction. The opening "You can" makes the whole effect optional to start; it does not make the first action optional once the effect is used.

"and if you do" / "then you can destroy" wording matters

Cards that negate by keying on destruction — Stardust Dragon ("a card or effect is activated that would destroy a card(s) on the field"), Stardust Spark Dragon, Dragonmaid Sheou-type negates — can only be activated in response to an effect that is going to destroy. Read connectors like "and if you do" and "then you can" exactly. When the destruction sits behind a "then you can destroy", it is optional destruction and not guaranteed, so at activation time the effect does not qualify as one that "would destroy," and these negators cannot be chained to it.

Centur-Ion Primera Primus — "… add 1 'Emblema' card from your Deck or GY to your hand, then you can destroy 2 cards (1 on each field)."

"Can Stardust Dragon negate Centur-Ion Primera Primus's effect?"

— Answer: No. The destruction is a "then you can destroy" follow-up — optional, not a guaranteed destruction — so the effect is not one that "would destroy a card(s) on the field" at the moment Stardust Dragon would respond. Stardust Dragon therefore cannot be activated against it. Contrast a mandatory "destroy 2 cards" with no "you can": that would destroy, and Stardust Dragon could respond.

Judge calls to watch for

• Read X's wording first: "as many as possible" needs ≥1 destroyed; named-target wording needs those targets destroyed.
• "do X, then you can Special Summon this card": if X (an add/search/etc.) is made impossible — Droll & Lock Bird, Ash Blossom, no valid target — the self-Summon is lost. Don't rule the monster comes back anyway.
• "You can Set/Search/Add X, then you can destroy/summon Y": if the required first Set/Search/Add has no legal application at activation, the effect cannot be activated merely for the optional follow-up.
• A "then you can destroy" clause is optional destruction / not guaranteed, so cards that respond to effects that "would destroy" (Stardust Dragon, etc.) cannot be activated against it. Only a guaranteed destruction qualifies.
• "ignoring Summoning conditions" and the destruction gate are independent — satisfying one does not satisfy the other.
• A monster surviving a "destroy" step because it cannot be destroyed is the usual reason a "then" follow-up silently fails.

Sources

• Illusion Gate text and rulings, Konami Yu-Gi-Oh! Neuron DB cid=21754
• https://yugipedia.com/wiki/Card_Rulings:Illusion_Gate
• Ame no Habakiri/Murakumo no Mitsurugi and Centur-Ion Primera Primus verbatim text via YGOPRODeck API ("then you can Special Summon" gated on the add from Deck
• "then you can destroy" is optional/not guaranteed, so Stardust Dragon — which responds to effects that "would destroy" — cannot be activated against it)