If someone is multiclassing a noncaster and a full caster class, that character will most likely will have more spell slots than which is known or which is prepared for it. So,it means that many of its spell slot are unused/empty. In this case,to cast spells at higher level seems a logical move, since it is possible to cast lower spells at higher level without being necesarry replacing any with one from a lower level,which happens in cases when there are no any unused/empty spell slot. (This usually happens when someone is not multiclassing.) So, I used to imagine that for example a 1 lvl spell which is casted 3rd level turn into a 3rd level spell, making the 3rd level unused/empty spell slot consumed. However my DM told me that this is not the case: if I have any spell slot at a given level that is empty/unused I can cast ANY spell which is under its spell level,and it DOES NOT consume the unused spell slot. So: if I have an empty/unused spell slot at the 3rd spell slot level, I can cast ANY first or second level spell at third level if I wish,only because exist one which is empty/unused,and I can do it with other lower spells,immediately after i have casted one on higher level. According to him,in this case the spell slots are only consumed at their original spell slot level. Since the PHB does not write anything about this,I've got to accept what my DM say,however I find it little strange.
What is your opinion?My DM is right or there something else that we have ignored?
If you cast a spell that is normally level 1, say, Burning Hands, with a 3rd level slot, then you use up that 3rd level slot, not the 1st level slot. You also do 5d6 damage instead 3d6 damage due to the specifics of that spell.
So a 5th level Wizard, if he's just started his day, would start off with:
4 First level slots, 3 Second level slots and 2 Third level slots.
After casting Burning Hands with a 3rd level slot, he'll have:
4 First level slots, 3 Second level slots and only 1 Third level slot left.
This is how it works for any spell. You can cast any spell with any slot you have available (that is equal to or greater than that spell's level), but some (most?) spells don't increase in effect. You can cast Shield with a second level slot, but it still gives the same effect because there is no mention of the spell becoming more powerful with higher level slots, unlike Burning Hands.
If you're not willing or able to to discuss in good faith, then don't be surprised if I don't respond, there are better things in life for me to do than humour you. This signature is that response.
Regardless of how many spells a caster knows or prepares, he or she can cast only a limited number of spells before resting. Manipulating the fabric of magic and channeling its energy into even a simple spell is physically and mentally taxing, and higher- level spells are even more so. Thus, each spellcasting class's description (except that of the warlock) includes a table showing how many spell slots of each spell level a character can use at each character level. For example, the 3rd-level wizard Umara has four 1st-level spell slots and two 2nd-level slots.
When a character casts a spell, he or she expends a slot of that spell's level or higher, effectively "filling" a slot with the spell. You can think of a spell slot as a groove of a certain size--small for a 1st-level slot, larger for a spell of higher level. A 1st-level spell fits into a slot of any size, but a 9th-level spell fits only in a 9th-level slot. So when Umara casts magic missile, a 1st-level spell, she spends one of her four 1st-level slots and has three remaining.
Finishing a long rest restores any expended spell slots.
Some characters and monsters have special abilities that let them cast spells without using spell slots. For example, a monk who follows the Way of the Four Elements, a warlock who chooses certain eldritch invocations, and a pit fiend from the Nine Hells can all cast spells in such a way.
Casting a Spell at a Higher Level
When a spellcaster casts a spell using a slot that is of a higher level than the spell, the spell assumes the higher level for that casting. For instance, if Umara casts magic missile using one of her 2nd-level slots, that magic missile is 2nd level.
Effectively, the spell expands to fill the slot it is put into.
Some spells, such as magic missile and cure wounds, have more powerful effects when cast at a higher level, as detailed in a spell's description.
linklite did a good job of describing it. Maybe the rules above could have made it more clear but they are there.
If someone is multiclassing a noncaster and a full caster class, that character will most likely will have more spell slots than which is known or which is prepared for it. So,it means that many of its spell slot are unused/empty. In this case,to cast spells at higher level seems a logical move, since it is possible to cast lower spells at higher level without being necesarry replacing any with one from a lower level,which happens in cases when there are no any unused/empty spell slot. (This usually happens when someone is not multiclassing.) So, I used to imagine that for example a 1 lvl spell which is casted 3rd level turn into a 3rd level spell, making the 3rd level unused/empty spell slot consumed. However my DM told me that this is not the case: if I have any spell slot at a given level that is empty/unused I can cast ANY spell which is under its spell level,and it DOES NOT consume the unused spell slot. So: if I have an empty/unused spell slot at the 3rd spell slot level, I can cast ANY first or second level spell at third level if I wish,only because exist one which is empty/unused,and I can do it with other lower spells,immediately after i have casted one on higher level. According to him,in this case the spell slots are only consumed at their original spell slot level. Since the PHB does not write anything about this,I've got to accept what my DM say,however I find it little strange.
What is your opinion?My DM is right or there something else that we have ignored?
I'm not sure I understood, so I'll start over.
If you cast a spell that is normally level 1, say, Burning Hands, with a 3rd level slot, then you use up that 3rd level slot, not the 1st level slot. You also do 5d6 damage instead 3d6 damage due to the specifics of that spell.
So a 5th level Wizard, if he's just started his day, would start off with:
4 First level slots, 3 Second level slots and 2 Third level slots.
After casting Burning Hands with a 3rd level slot, he'll have:
4 First level slots, 3 Second level slots and only 1 Third level slot left.
This is how it works for any spell. You can cast any spell with any slot you have available (that is equal to or greater than that spell's level), but some (most?) spells don't increase in effect. You can cast Shield with a second level slot, but it still gives the same effect because there is no mention of the spell becoming more powerful with higher level slots, unlike Burning Hands.
Does that answer your question?
If you're not willing or able to to discuss in good faith, then don't be surprised if I don't respond, there are better things in life for me to do than humour you. This signature is that response.
Yes,it did,thank you.It seem that my DM was not clear enough,I have misunderstood something.
By the way,it is a sad thing that the PHB does not explain things so clearly as you do.
The 5E system is among the best systems,but the way how the PHB explain it is oftenly a complete disaster.
From the rules on spell casting
linklite did a good job of describing it. Maybe the rules above could have made it more clear but they are there.
EZD6 by DM Scotty
https://www.drivethrurpg.com/en/product/397599/EZD6-Core-Rulebook?