Ok as you might have known in advanced play..chaining also occurs of cards of speed 1,2 and 3. All Spells are Spell Speed 1 (with the exception of Quick-Play Spells (Spell Speed 2).
Speed types:
Spell Speed 1 is the slowest of all the Spell Speeds, and is the only Spell Speed that cannot be countered by cards of the same Spell Speed during normal play.
The following are all Spell Speed 1:
Normal/Field/Continuous/Equip & Ritual Spell Cards Continuous/Ignition/Trigger & Flip Monster Effects The only case in which Spell Speed 1 effects can be chained against each other, is when they activate simultaneously i.e. 2 "Mystic Tomatos" attacking each other, or 2 "Sangans" attacking each other, with each effect activating in the Graveyard.
Spell Speed 2 cards can be used against Spell Speed 1 and other Spell Speed 2 cards.
The following are all Spell Speed 2:
Quick-Play Spell Cards Normal & Continuous Trap Cards, Quick Monster Effects (cards with piority first-not monarches as they have to be tributed summoned SUCCESSFULLY)
Spell Speed 3 cards can be used against Spell Speed 1, Spell Speed 2, and other Spell Speed 3 cards. Spell Speed 3 cards can only be countered with other Spell Speed 3 cards. Therefore, you cannot counter "Negate Attack", "Magic Jammer", "Trap Jammer" or "Magic Drain" with "Royal Decree".
The only cards that are Spell Speed 3 are Counter Trap Cards.
Thus SS1 can only chain SS1, SS2 can chain SS1/2 and SS3 chains up all, thats why solemn judgement has such a high cost.