Multiclassing Cleric LvL 4 with Warlock lvl 1

Question

I am having a nice argument with my buddy about multiclassing. I am new to the game so there is a lot of things I don't know, he is quite versed though. Our argument is centered in the amount of LvL 1, LvL 2 and LvL 3 Spells I can have. As my character is LvL 4 Cleric and LvL 1 Warlock, I assume he is LvL 5 in total. So checking the Multiclass Spellcasting Table, it says he has access to:

4 LvL 1 spells, 3 LvL 2 Spells and 2 LvL 3 Spells.

Counting that Warlock Pact Magic allows the character to use the Warlock spell slots as Warlock Spells or Cleric Spells, he says that the LvL I have from the Warlock doesn't allows me to have the amount of spells I quoted above, because I am still a LvL 4 Cleric, so I can't use LvL 3 Spells, neither use a LvL 2 Spell as a LvL 3. So the amount of spells I have according to the multiclass table is the one of a LvL 4:

4 LvL 1 spells and 3 LvL 2 Spells

Our main problem is related to how we mix Warlock to the Multiclass table.

Answer 1

You don't use the multiclass spellcasting rules

The multiclassing rule for the spellcasting feature (which gives you spell slots based on the Multiclassing Spellcaster: Spell slot table) because it only comes into effect:

Once you have the Spellcasting feature from more than one class, use the rules below. If you multiclass but have the Spellcasting feature from only one class, you follow the rules as described in that class.

--- Player's Handbook, p. 164

Notably, Warlocks don't get a Spellcasting feature, they get a differently named feature called Pact Magic. Thus your spell slots aren't replaced by the multiclassing rules, but instead added from your two sources of spell slots. This gives a Cleric 4/Warlock 1 character 5 × 1st level slots and 3 × 2nd level slots.

Thankfully, due to the multiclassing rule on Pact Magic (also page 164 of the PHB) you can use the different slots interchangeably for casting, but note that the Warlock slot will recharge on short rests and the Cleric ones on a long rest.

Answer 2

If you look in the rules for multiclass spellcasting, it has a section dedicated to pact magic (which is what you have as a warlock)

Pact Magic. If you have both the Spellcasting class feature and the Pact Magic class feature from the warlock class, you can use the spell slots you gain from the Pact Magic feature to cast spells you know or have prepared from classes with the Spellcasting class feature, and you can use the spell slots you gain from the Spellcasting class feature to cast warlock spells you know.

As a 4th level Cleric you have 4 1st level and 3 2nd level spell slots that replenish on a long rest. You can use these slots to cast spells from either class as long as you know them. And as a 1st level Warlock you have a single first level spell slot that replenishes on a short rest. You can use this slot to casts spells from either class just as you can with the slots you get from Cleric.

Answer 3

Your DM is correct in that you do not have level 3 spells, but you should have 5 level 1 spells and 3 level 2 spells. The 5 level 1's are the 4 from Cleric and 1 from Warlock.

Since Warlock's use Pact Magic and not Spellcasting, you do not use the multiclassing table. You simply add have your Cleric spell slots and your Warlock spell slots. Now, that being said you can use either set of spell slots to cast any of your spells. Just be sure to keep track of which classes spells you are using, since the spell casting modifier (attack roll and save dc) is dependent upon the spell being cast and not the spell slot being used.

EX. Casting Hellish Rebuke (a Warlock Spell) using a Cleric spell slot still uses your Charisma modifier.

Relevant section from the Multiclassing Section in the Basic Rules:

Pact Magic. If you have both the Spellcasting class feature and the Pact Magic class feature from the warlock class, you can use the spell slots you gain from the Pact Magic feature to cast spells you know or have prepared from classes with the Spellcasting class feature, and you can use the spell slots you gain from the Spellcasting class feature to cast warlock spells you know.

And here is the Spell Slot rules, as you can see, no mention of Warlock:

Spell Slots. You determine your available spell slots by adding together all your levels in the bard, cleric, druid, sorcerer, and wizard classes, and half your levels (rounded down) in the paladin and ranger classes. Use this total to determine your spell slots by consulting the Multiclass Spellcaster table.