What are these "differences" you are talking about?
As I said earlier, one of them is that Solemn Warning can only negate Summons or cards that Summon. But that's not all there is to it. There's quite a lot of cases in which Solemn Judgment is useless. Why? Because Solemn Judgment can only negate Inherent Summons and Normal Summons, not Summons by Card Effects, while Solemn Warning can negate both. Summons by Card Effects cannot be negated, however, you can negate the effect that causes the Special Summon. This means that cards like Solemn Judgment, Thunder King Rai-Oh, etc... cannot negate Monsters summoned by cards like Monster Reborn, Wind-Up Magician, Rescue Rabbit, etc...

What is the difference between an Inherent Summon and a Summon by Card Effect?
An Inherent Summon is a Special Summon that happens due to a condition listed on a card, and it does NOT start a chain. A Summon by Card Effect, unlike Inherent Summons, starts a chain. Examples of Inherent Summons are: Black Luster Soldier - Envoy of the Beginning, Dark Armed Dragon and Chaos Sorcerer. Some examples of Summons by Card Effects are: Mermail Abyssmegalo (summoned by it's own Effect), Tragoedia (same as Abyssmegalo), Gorz the Emissary of Darkness (same as Abyssmegalo), Monsters summoned by Monster Reborn, Call of the Haunted and Wind-Up Magician.

How do I recognize Inherent Summons?
By just reading the card. In cards with PSCT (problem solving card text), effects that start a chain have a semicolon ( ; ) to indicate that they do (e.g. Mermail Abyssmegalo). Usually, cards that have a semicolon in their Summoning Effect aren't Inherent Summons. If the card doesn't have PSCT, it's a bit harder to tell if it's an Inherent Summon or not. Although, there is an easy way to check. Simply go to the Yu-Gi-Oh! Wikia and search the card there. Then look for "Card effect types" on the right of the card. Check which effect the summon is, and if it says "Summon", then it's an Inherent Summon. If it says "Trigger" or "Ignition", it's not.

Tell me more about Solemn Warning.
Solemn Warning does not negate effects. You heard that. It only negates the Activations of Effect Monsters effects or the Activation of a Spell or Trap Card. That's the most simple way to explain it. Why does it matter? Let's take, for example, Valhalla, Hall of the Fallen and Solemn Warning. One player has Solemn Warning face-down. The other Player activates Valhalla, Hall of the Fallen. Now, most of you think the Player who controls a set Solemn Warning can negate the summon of the monster the other Player summons with Valhalla, but you're incorrect, because of what I just said. Now you may be thinking, "so I can only negate Valhalla?". That's also incorrect. you cannot negate the activation of Valhalla because it does not Summon anything when the card is activated. This is a tricky situation, but that's all there is to it. Although don't get me wrong here, Solemn Warning CAN negate cards like Starlight Road and Spellbook Judgment Day, because, even though they don't summon as soon as they're activated, they still summon at the resolution of their effects. While Valhalla is already face-up on the field when you decide to activate it's summoning trigger-like effect, so Solemn Warning cannot negate the card activation (since the card has already been activated). Yeah... pretty hard, isn't it?

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