Every RTS game should have a baseline of functionality, like so:
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Mouse and Keyboard
In representing the systems of the world, there are physics, magics, and other varying mechanics...
Here, "neutral" does not mean "no additional effect" but rather "no bonus or negative effect." Orthogonal generally means the same thing as neutral except that now both elements are in play at the same time, neither helping or hurting the effectiveness of the other.
Further, while it is common to represent "cold" and "dark" and other "elements" individually, they cannot truly be separated from "heat" and "light," etc. So in this table, "heat" represents the entire temperature spectrum, "water" represents the entire humidity spectrum, and so on. Clearly, the goal of mastering an element in a combat sense is to be able to change a target's composition in a damaging way, so the polar opposites of each element are the most interesting. But clearly, when considering, say, a master of the heat element, neither complete cold nor complete heat should have much affect on it, but instead another element or attack would be effective.