There are a number of special rules attached to D&D 5E spell-casting that may not immediately be apparent when reading through the Player’s Handbook. This article looks at a few of those things.

Somatic Components

Most spells have a somatic component, which is to say, they require hand movements. The rules in 5E state that you need one hand free to cast these spells.

If you’re wielding a two-handed weapon then you can hold the weapon in one hand as your other hand casts the spell.

What if you’re wielding a weapon and a shield? Can you then cast a spell requiring a somatic component? The answer is: it requires some juggling.

You are allowed one free manipulation of an object each turn. This means you can sheathe your weapon or draw your weapon for free – but you can’t both sheathe a weapon and draw a spell-casting focus. If you sheathe a weapon, it then takes you an action to draw a wand. This sharply limits what you can do. In general, dropping an object doesn’t count as your free action (The Sage), so you could drop your sword at your feet and draw your wand, but it’s still clumsy.

Eldritch Knights and Clerics are most likely to be affected by this. However, assuming the spell doesn’t require the focus to cast, it’s very easy to take up the following pattern: Round 1: Sheathe weapon, cast spell with free hand. Round 2: Draw weapon, attack with it. That retains the limit of one item manipulation per turn while allowing alternating between weapon and spell-casting.

Keeping strictly to this rule also works against casters, Eldritch Knights in particular, casting the shield spell as a reaction in the middle of combat when already wielding a weapon and a shield.

Somatic and Material Components

There is an exception to the “you need a free hand” rule when casting Somatic spells: if the spell requires a material component, your “free hand” can hold your spell-casting focus (The Sage). 

A cleric or paladin who inscribes their shield with their holy symbol can use their shield as their spell focus. This option is given in the Player’s Handbook (page 151, Holy Symbol).

However, It still doesn’t allow them to cast Somatic spells with no Material components with a weapon in one hand and the shield in the other, though.

The solution to all of this? Take the War Caster feat – it allows you to cast spells that need somatic components even when both your hands are holding a weapon and shield.

Number of Spells per Turn

How many spells can you cast in a turn? If you can cast one as a bonus action, then the answer is generally “two”, but there are a couple of considerations.

The major one is this: If you cast a spell with the casting time of a bonus action, then the only other spell you can cast this turn is a cantrip with the casting time of 1 action (PHB pg 202). You are not allowed to cast (say) healing word and cure wounds in the same turn.

This rule also applies when a sorcerer uses their metamagic ability to Quicken Spell: the spell becomes 1 bonus action in casting time, and so you are limited to only casting a cantrip in the remainder of the turn. (Source: Jeremy Crawford, “The Sage”)

What about Action Surge?

A particularly odd interaction comes from a character using the fighter’s Action Surge ability to cast spells. In this case, you can cast two spells that require an action, because neither is a bonus action! However, if you cast a spell that takes a bonus action, your other two spells must be cantrips! (Source: Jeremy Crawford, “The Sage”)

How about reactions?

There are a few reaction spells that can be cast during your turn; the most typical use I see is a player using counterspell to counter the counterspell an opponent has used on the player’s first spell.

This is fine. You can cast both a regular spell and a reaction spell in the same turn. What you can’t do is use a reaction spell in the same turn you cast a bonus action spell. At that point, the bonus action spell rule comes into play, and the only other spells you can cast are cantrips with a casting time of one action.

As using a reaction spell uses your reaction, and you only regain that at the start of your turn, you can’t cast two reaction spells in the same round. You can’t counterspell in your turn, then cast shield during the ogre’s turn.

Concentration

In the earliest editions of D&D, casting a spell took a long time, and if you were struck before casting the spell, you lost the spell.

In 3E and 5E, casting a spell doesn’t take that long, but being struck while concentrating on an ongoing spell might cause it to be lost. The rules for this are pretty easy and you probably know them already: make a Constitution saving throw when you take damage; the DC is 10 or half the damage you took, whichever is higher.

Once again, the War Caster feat makes all of this a lot easier, as you now have advantage on those saving throws.

It is, however, worth pointing out the other parts of casting spells that requires concentration:

• You may only concentrate on one spell at a time.
• Spells that take more than one action to cast require concentration during the casting, meaning you can’t maintain another concentration spell when casting them, and you could lose the spell if you’re damaged in the meantime. The good news is that you don’t lose the spell slot if you don’t successfully cast the spell.
• If you ready a spell to cast when some trigger occurs, this also requires concentration. Note that you can only ready spells that have a casting time of 1 action, and they use your reaction to cast. Once again, you can lose the spell if you take damage in the meantime. In this case you do lose the readied slot.
• The Mage Slayer feat means that when its possessor damages a spell-caster, the spell-caster has disadvantage on their Constitution saving throw.

So, that’s a few items of interest I’ve noticed when playing the new edition of D&D.