When diction in a poem is considered, the various kinds of diction relate to the choice of words that the poet employs in his or her work and the level of that vocabulary in terms of formality and complexity. The best description of the diction in "Digging" is middle diction, because the language Heaney uses in this poem is not overly formal or elevated, as it would be if it were formal diction or poetic diction. However, at the same time, it is not informal diction, because colloquialisms and slang are not used in his description of his father and grandfather and their work. Consider the following quote from the poem and the kind of language that is employed:
Under my window, a clean rasping sound
When the spade sinks into gravelly ground:
My father, digging.
The language is correct and "proper English," but at the same time it is phrased in such a way that is easily understood, and conveys meaning that won Heaney a very wide readership and ensured that his poems were and are studied in schools across the United Kingdom. It is this simplicity of his vocabulary that allows his poems to have such a strong impact, as he is able to communicate meaning directly and without the obfuscation of more formal or poetic diction that would otherwise make discerning the theme or message of his work a more difficult task. However, the level of diction of his work in no way makes his poetry unchallening or too easy to read: by contrast, there is much to be analysed and studied in this poem and in all of Heaney's works as he builds up meaning and develops it through his careful word choice.