Can the Magus cast a spell using the Spell Combat feature while holding a one-handed weapon with two hands?

Question

The Magus' Spell Combat feature says in part:

To use this ability, the magus must have one hand free (even if the spell being cast does not have somatic components), while wielding a light or one-handed melee weapon in the other hand.

Does that mean you could cast the spell holding the weapon in 1 hand (since you can do this in any order), then use a free action to grip the weapon with 2 hands again, and then attack?

An example sequence of events:

1. hold longsword in 1 hand
2. cast spell
3. regrip with 2 hands
4. attack

Answer 1

It’s unclear, and ultimately you’ll have to ask your GM. It seems unlikely that the authors would have bothered requiring a free hand if it was intended to be so easy to work around that limitation, but that is speculation on my part. The official rules themselves do not give us enough information to be sure.

The issue is that it says

To use this ability, the magus must have one hand free [...] As a full-round action, he can make all of his attacks [...] and can also cast [...]

So the hand must be free for “this ability,” and “this ability” is defined as the full-round action taken to attack and cast. You can take free actions in the middle of full-round actions—that is, it is possible to grab the weapon with your other hand in the middle of your spell combat—but it isn’t clear what happens if you do that.

This is part of a broader under-specification in the rules: do things that have some requirement get interrupted if that requirement is lost in the middle of it? For example, if a spell changes an elf into a fiend, does an existing charm person effect “fall off” them (since charm person could not target a fiend in the first place)? There are games that explicitly get into these kinds of questions, but Pathfinder isn’t one of them. So, likewise, we don’t know—don’t even really have firm precedent for—whether or not losing a free hand in the middle of spell combat somehow messes up spell combat. For that matter, if it does mess things up—and as I speculated above, this does seem the more reasonable expectation—what exactly happens?

Personally, I would probably say the most consistent ruling is to say that, in that case, you are no longer using spell combat, and as a result you are either making a full-attack, or you are casting a spell. If you’re making a full-attack, you get all your attacks, but don’t cast any spell. If you’re casting a spell, you only use a standard action, but you don’t get any attacks. If you have already cast the spell and already made one or more attacks, then instead your action just ends and you give up any remaining attacks. The rules don’t specify this but it seems like the most consistent way to rule things in my view.

That said, to get even more subjective/personal, I personally don’t see a whole lot of value in the free hand requirement on magus. I don’t think it adds very much to the game. I’m happy enough to waive it most of the time—magus is a decent enough class, but it certainly isn’t especially high-power, and it doesn’t bother me to allow them to do use a two-handed weapon. For that matter, it doesn’t bother me to allow them to dual wield, either. I’m fine with a magus performing somatic components with a weapon in hand, that seems reasonable for someone with their specialized training. This is emphatically not the rules—it appears the authors did have problems with magi doing those things—but personally I’m fine with giving them as a buff.

Answer 2

Spell Combat continues:

A magus can choose to cast the spell first or make the weapon attacks first, but if he has more than one attack, he cannot cast the spell between weapon attacks.

This strongly implies that casting the spell and making the weapon attacks aren't "simultaneous", but that one necessarily happens before the other. Therefore, the question becomes whether a character holding a weapon in two hands can release and re-grasp it with one of those hands during a round. Fortunately, Paizo's Pathfinder FAQ covers this:

Two-Handed Weapons: What kind of action is it to remove your hand from a two-handed weapon or re-grab it with both hands?
Both are free actions. For example, a wizard wielding a quarterstaff can let go of the weapon with one hand as a free action, cast a spell as a standard action, and grasp the weapon again with that hand as a free action; this means the wizard is still able to make attacks of opportunity with the weapon (which requires using two hands).

As with any free action, the GM may decide a reasonable limit to how many times per round you can release and re-grasp the weapon (one release and re-grasp per round is fair).

Therefore, barring the magus trying to take other actions which the GM rules would preclude doing so, the magus should have no difficulty in having a free hand to cast spells using Spell Combat and still wielding a weapon with both hands.

This is incidentally covered by this answer.