The somatic component was a basic part of spellcasting. Many spells required the caster to make a motion to cast the spell. If the caster was unable to make the correct motion, the spell could not be cast. Wearing armor or using a shield interfered with the somatic components of arcane spells, creating a risk of spell failure. Bards and some other arcane classes could cast spells in light armor without this risk, because their somatic components were less elaborate. Each spellcasting tradition had its own somatic components.