“Digging” doesn’t have a regular metrical scheme, which makes the poem an example of free verse. However, a closer look at the ways Heaney uses meter throughout the poem helps understand what he’s doing in a more nuanced way. Let’s begin with the five lines that open the poem:

Be-tween | my fin- | ger and | my thumb [iambic tetrameter] 

The squat | pen rests; | snug as | a gun. [iamb, iamb, trochee, iamb]

 

Un-der my | win-dow, | a clean | rasp-ing sound [dactyl, trochee, iamb, anapest] 

When the spade | sinks in- |to gra- | velly ground: [anapest, iamb, iamb, iamb] 

My fa- | ther, digg- | ing. I | look down. [iambic tetrameter]

Start by noting that lines 1 and 5 are both examples of regular iambic tetrameter, featuring, as they each do, a series of four iambs. (Recall that an iamb is a metrical foot consisting of one unstressed syllable and one stressed syllable, as in the word “be-tween.”) The middle lines each have a unique metrical structure. Though irregular, these lines are nonetheless built with a series of iambs as well as other metrical feet, such as trochees (stressed–unstressed), dactyls (stressed–unstressed–unstressed), and anapests (unstressed–unstressed–stressed). Despite being irregular, the meter in these lines and throughout the rest of the poem demonstrate an important point about the speaker’s poetic craftsmanship. He carefully manages the rhythm of the language in the poem on a line-by-line basis. But just as he refuses to follow in the path of either his father or grandfather, he also refuses to subscribe to any one metrical tradition.