Can I cast a spell in combat check after having rolled?

Question

In the Arkham Horror board game, consider the following:

I am about to do a combat check fighting a monster. I already decided I want to use a spell in combat (e.g. "Wither"; it is untapped, I have enough hands). Can I roll the dice without casting the spell at first and if it is not enough, try casting the spell and (if successfull) roll additional dice?

I could not find a convincing answer in the rules and FAQs. It definitely states two different things:

• In order to use spells, you have to have enough hands
• In order to gain their bonuses, you have to successfully cast them

So while you have to decide on the choice of your weapons / spells / hands before a combat check, just carrying a spell (or, more accurately, "spellbook") into combat does not seem to force you to cast it. Moreover, using hints works exactly this way (you can choose to use them to roll additional dice).

Is there any information on this that I have missed? I know the question might seem odd at first, but the longer I think about it, the less sure I am about the answer.

Answer 1

From the Rules (Page 13)

Skill Checks / Modifiers This number is added to or subtracted from the investigator’s skill value before the player makes the check. The result is the number of dice the player rolls to make the check. Note that modifiers always apply to the number of dice a player rolls for a check, not to the results of the individual dice.

A combat check is a skill check, and a spell is a modifier (with additional rules) to that check, therefore you must decide to use the spell before rolling the combat check, and you can not change your mind after the check to roll additional dice if you failed.

Thematically it makes sense as well, spells are hard to cast, require preparation and mental strengthening, so it's best to have them at the ready and in hand.