Fire and water are considered to be polar opposite elements, classically and in alchemy and traditional magical practice. They are sometimes considered to be the two primordial elements, the combination of which gave rise to the other two elements of earth and air. Fire and water are also the elements most associated with Sun and Moon, and thus the Horned God and the Goddess within Wicca. For this reason, covens that associate the athame with air (and the wand with fire) may decide to use the wand to bless the wine chalice, instead of using the athame. A union of air and water does not carry the same symbolic significance of the "conjunctio oppositorum" (union of opposites) that the union of fire and water does. Also, covens that regard the athame as air and the wand as fire may choose to cast the ritual circle with the wand or staff, instead of the sword or athame—if they conceive of this casting in the traditional way, as a casting of etheric fire via a projection of psychic energy. If they conceive of the circle casting as cutting a line in the air with the tool of air, then they may choose to purify the circle with the remaining three elements of fire, water, and earth; this would involve using a candle to purify the circle, and omitting the incense, since the circle has already been imbued with the element of air.