Compare the poetic methods used by Heaney in sonnets 1 and 3 of "Clearances."
Both poems deal with Heaney's mother who is deceased.
Sonnet one and three are very different pieces, and though both are set in the past, the first deals with the distant past and how the author is tied to his mother's family history through the years, though he was not directly a part of that history.
The second of the sonnets, number three, deals with the recent past by comparison, of time he spent with his mother, creating an exclusive memory with her while the rest of the family was at mass.
The poetic methods (devices) that appear to be used in the first sonnet are hyperbole and an extended metaphor.
Hyperbole refers to exaggeration; the poet seems to be saying that a rock thrown a hundred years ago continues toward its target—now the poet, though it was originally aimed at his great-grandmother. (The sense is that something started years ago still is reverberating into the future.)
An extended metaphor is simply a comparison that goes beyond a simple statement to continue through a passage or "extended" piece of writing.
The passage here describes the casting of a rock (cobble) which startles a horse that takes off in a riotous race carrying his great-grandmother's trap (a small carriage); the horse and all go flying through a town at a "panicked" gallop down a hillside (brae) through a "gauntlet" of insults (a crowd of disapproving neighbors—perhaps near the church—?). The cause seems to be that the woman changed her religion ("The Convert." "The Exogamous Bride") and is attempting to go to mass for the first time.
The comparison is of the fervor caused by something his ancestress did in her lifetime that moved along like a horse gone wild.
The race conveys the sense that the mad dash brought on by a careless or angry hand throwing a stone catapults the woman through the difficult decisions she has made (not allowing an easy transition on her part), and that decision is still affecting the poet so many years later. However, as if pulling the reins on the runaway horse, the poet slows the motion of the poem with the pivotal word "anyhow." It is as if the speaker says, "This has gone on long enough, and it stops here."
What has been left to the poet, he notes, after the death of his mother is not what one might expect: silver or Victorian lace, but the need to exonerate those who have been judged all this time in a "race" that began many years ago based on a preference his great-grandmother exercised to worship as she saw fit.
Sonnet three is a little more straightforward. In the first eight lines we see a simile describing the potatoes peeled:
...let fall one by one
Like solder weeping off the soldering iron:
Next is a metaphor describing the peeled potatoes sitting in a bucket of clean water:
Cold comforts set between us, things to share / Gleaming in a bucket of clean water
Onomatopoeia is used with little pleasant splashes.
There is a pivotal shift found at the beginning of the ninth line, where the scene changes in the writer's memory, to fast forward to his dying mother's bedside.
A metaphor (and idiom) is used with:
"Went hammer and tongs at the prayers for the dying,"
indicating that the priest is working energetically administering the late rites.
In line thirteen, beautiful imagery is used in remembering how they peeled the potatoes together "...our fluent dipping knives."
Also, in this last section (known as the "sestet"), we hear end rhyme used twice, where it has not been used before, perhaps providing an auditory focus for the listener to tie the "before" memory with the "last" memory: "dying...crying," and "knives...lives."
The pace of the first sonnet is maddening, while the rhythms of the third sonnet are warm, inviting and endearing.