[quote=@Sen]
Some would call it more than just bromantic. I'm not sure how I feel about the deeper end.

So let me get this straight:
The way this magic (magery, I guess) works is that you need an element to use an element, as explained in the firewood analogy. As for the fire example you stated you can basically use the temperature of one's surroundings to fuel a flame. My question is, how much of your environment can you use? If someone was in, say, -50 weather in some ice cave, could they still conjure a large fireball or whatever through the temperature (and some good old Magi magic) and make all that ice even more frozen? 

Is there an actual limit to the resources you can use or are Magi supposed to use their own discretion?

Or am I getting this all wrong?
[/quote]
Well I don't know either but the jamming out in the Church was pretty awesome.  

You've actually got the general idea of it down pretty well. Basically how it works is this.

You have a magi, a desired effect, lacrimas, and outside energy.

Let us say a magi wants to make fire as you said like lighting a candle something real basic.

Your Desired effect would be: a lit wick right?

Well how you get there is basically broken down into the equation of Magi+ lacrimas + outside source (in this case for fire some sort of heat source) = desired effect.

So your magi is the catalyst that gets everything moving because they draw the other parts of the equation into them to basically channel to produce the magery. 

Lacrimas or the natural base energy floating in the air the comes out of leylines is drawn in by a magi. Depending on their level of lacrimas control essentially their inherent natural born ability to act as reservoir to hold this energy and use it. A magi with more control and hence able to hold more lacrimas in their body will require less work provided by the outside source. For example with a C- level of control (the average of most magi) lacrimas does about 50% of the work in this equation. While somebody like Solomon the only S+ level would have his lacrimas do about 99% of the work.

Outside sources are funny in that basically the less abstract the source is the stronger it is. Meaning that it will take less energy to draw the heat required out of say another lit candle to create the small spark because the fire is a real tangible thing that you can feel and see. Or you could draw the heat from your body which is dangerous because you could kill yourself if you overdraw but to light a candle stick you should be fine. Using the temperature in the air though that is harder because the idea is starting to become more abstract and so while you can drag the temperature out of an area so that the resultant area would cool down to create your fire, a Magi could totally do that though in -50 the heat would very minimal and not provide a lot of get up and go. But it requires more skill because to perform something like this effectively and not tiring yourself out in the process you need more lacrimas control, becaus more lacrimas means less of heat of the air you need to drag out so less stress on your mind. Hell B+ Ranks about as high as most people will see of people in Lacrimas control will even go as far as dragging the geothermal heat of the earth rather than the air because their lacrimas provides most of the energy so they only need a little bit of outside source to fuel something.

Sorry if that got a bit wordy at the end but that should help clear things up a little bit. Basically the more abstract and devoid from the physical self the harder it is to use as a source. 

Magi really don't have limits per say they can draw as much as they want but this provides great mental and physical strain on the body to continually draw from the source and process it through their tainted blood. I.E if somebody tries to go God Mode their own internal lacrimas reservoirs would not be able to handle it and their brains would explode. :)