"I cease to find anything more aggravating than dedicating your upholstery to honor a new Element, only to discover it has ceased to exist a day later."
Many Elements exist in a quasi-confidence. Not concrete enough to be a solidified staple of the cosmos, but not uncertain enough to remain theory. They fluctuate between being and not being, which can be truly aggravating for Elementologists trying to record the damn things. Elements can be divided depending on two axes. The Tangibility Axis, and the Certainty Axis.
The Tangibility Axis
Tangibility is how physical the Element is in our reality. Namely, if you are capable of throwing it at someone's head and causing enough physical or emotional injury to be measured. The Element of Rock, for example, is considered concrete on the Axis. While the Element of Nostalgia is abstract.
The Certainty Axis
Certainty is how confident the Element is with its position in the cosmos. The more Certain the Element, the Less likely it is to fluctuate from the constant beratement of Casters. The Element of Fire is respected and deeply grounded in our reality, where something like the Element of The Outrage Over Children's Novels aren't quite as sure of Its capabilities and blips in and out of existence far more frequently than it would care to admit. We Researchers call this "Performance Anxiety."