Although strictly speaking, iambic pentameter refers to five iambs in a row (as above), in practice, poets vary their iambic pentameter a great deal, while maintaining the iamb as the most common foot. However, there are some conventions to these variations. Iambic pentameter must always contain only five feet, and the second foot is almost always an iamb. The first foot, in contrast, often changes by the use of inversion, which reverses the order of the syllables in the foot. The following line from Shakespeare's "Richard III" begins with an inversion: