Sentiment/value based magic system

I was reading the So you want to/write a functional magic system and it got me thinking. At one point I considered using an Equivalent Exchange based cost and the page mentions sentimental value. This brings me to my question:What would the scope of sacrificing something of sentimental value be in terms of magical power? Before someone decides to be a smart@$$ and says it's "Big" I know that at least. What confuses me is just how big.

I would imagine that it could vary from magic system to magic system. Maybe magic is extremely demanding, and requires huge sacrifices for even small effects; maybe it's generous, and even a small sacrifice can gain a powerful effect.

(I could even see a magic system in which the value-conversion is inverted: small sacrifices produce large effects, while small effects require heavy sacrifices.)

I mean I get that but the point is that they are equal. Let's say you sacrifice a family heirloom that has been around for multiple generations, how big of an output would that bring?

It’s your system, that’s for you to decide.

You could say that it's equivalent to the amount of emotional residue contained in the item. Something or someone had to value it for a period of time, the more people, the more time, and the more valued, the more power it renders. You could even develop an algebraic formula to illustrate this.

Since emotional weight isn't inherently magical power, it seems to me that there's either a conversion to be done, whether it's an in-universe turning of emotional weight into magical power, or an out-of-universe determination that in the setting emotional weight is in fact a form of magical power, and that it has some particular scale. Either way, different settings might have different conversion-factors.

If you're stuck, perhaps try thinking about what feels "right" to you. Does a family heirloom feel like enough to make a small glimmer of light? To open a portal? To conjure an entire city? Even more than that?

Edited by ArsThaumaturgis on Jun 10th 2019 at 4:18:08 PM

I suppose it depends on how the caster themselves feels about the item, you might look at a penny and think it's worthless so any sacrifice made of it would be proportionately puny. If however that penny was a priceless heirloom passed down from generations then it might have more sentimental value depending on if said caster places any geniune feelings into it. Slightly off topic but I also wanted to introduce a sort of magical overload to prevent people just carelessly destroying artifacts for power.

In a story that I planned but never wrote, churches are concentrations of great spiritual and magical power, due to the effect of so many believers having prayed and worshiped there. It's like their emotional auras became embedded into the walls and furnishings over the generations, available to any magic user who understands the principle, and can forge magic that was compatible with the belief system of the church members.