Even if magic and mundane physics are fundamentally different, that doesn't necessarily help if both are being applied to the same 'stat'.
I agree no solution is perfect, but I'm not aiming for perfection, we have a problem and I'm just trying to identify the better solution out of the possible options as per the original post and it's good news that we have several options as that is better than none! So, taking a step back, lets clarify the problem and the solution options and make sure that we all agree on what we are trying to solve and how
Problem: It isn't clear from the rules / card text how in a situation where both Fear and Courage are in play the two interact
(Chaos Spell) Fear - This spell causes any one hero to become so fearful that his attacks are reduced to one combat die. The spell can be broken by the hero on a future turn by rolling one red die for each of his mind points. If a 6 is rolled, the spell is broken.
(Hero Spell) Courage - This spell may be cast on any one hero, including yourself. The next time that hero attacks, he may roll two extra combat dice. The spell is broken the moment a hero can no longer "see" a monster.
Couple of examples to clarify
Example 1:
1. On Barbarian's turn: Barbarian wielding Battle Axe (4AD) boots open door to room revealing a few Skeletons and a Dread Sorcerer and decides to stay put
2. On Wizard's turn: Wizard casts Courage spell on Barbarian (4AD+2AD=6AD)
3. On Zargon's turn: Dread Sorcerer casts Fear spell on Barbarian
4. On Barbarian's turn: he attacks Skeleton, how many AD does he roll?
Example 2:
1. On Barbarian's turn: Barbarian wielding Battle Axe (4AD) boots open door to room revealing a few Skeletons and a Dread Sorcerer and decides to stay put
2. On Zargon's turn: Dread Sorcerer casts Fear spell on Barbarian
3. On Wizard's turn: Wizard casts Courage spell on Barbarian
4. On Barbarian's turn: he attacks Skeleton, how many AD does he roll?
Two possible solutions identified so far:
Solution A - some general rule of precedence logic is applied that means that the sequence in which the actions happen is used to determine the combined effect (possible involving differences based on temporary/permanent effects and/or magic/mundane effects) - I'll let supporters of this option better define this rule but I think it was KK that first stated it as follows:
A spell is cast and takes effect as per its wording, then another is cast and takes effect as per its wording.
That is to say that it is the order in which they were cast that matters.
In example 1: that would result in the Barbarian rolling 1 AD
In example 2: that would result in the Barbarian rolling 3 AD
Solution B - modify the Fear spell card so that it reads "his weapon-based attack dice are reduced to one" instead of current "his attacks are reduced to one combat die"
That is to say that Fear reduces your number of combat dice rolled in attack due to your weapon to 1 but Courage gives you a +2 on top of your weapon attack strength (so the above suggested card text modification clarifies that)
The sequence doesn't matter so the outcome of both examples would be the same
In example 1 and 2: that would result in the Barbarian rolling 3 AD
Solution C - modify the Fear spell card so that it reads "his attacks are reduced by two combat dice" instead of current "his attacks are reduced to one combat die"
That is to say that the effects of Fear and Courage are opposites, Fear -2AD, Courage +2AD
The sequence doesn't matter so the outcome of both examples would be the same
In example 1 and 2: that would result in the Barbarian rolling 4 AD
Once we are happy with the above then we can see how the three options play out in other examples than the ones already provided that might be relevant