Let’s use the same passage in my review to examine Heaney’s translation more closely. Lines 702b–09 of poem read (I picked this passage pretty much at random, but it turned out to be really fruitful in demonstrating both the deficiencies of Tolkien’s translation and how Heaney makes the poem his own):
Com on wanre niht
scriðan sceadugenga. Sceotend swæfon,
þa þæt hornreced healdan scoldon,
ealle buton anum —þæt wæs yldum cuþ
þæt hie ne moste, þa Metod nolde,
se scynscaþa under sceadu bregdan—
ac he wæccende wraþum on andan
bad bolgen-mod beadwa geþinges.
Which Heaney renders as:
Then out of the night
came the shadow-stalker, stealthy and swift;
the hall-guards were slack, asleep at their posts,
all except one; it was widely understood
that as long as God disallowed it,
the fiend could not bear them to his shadow-bourne.
One man, however, was in fighting mood,
awake and on edge, spoiling for action.
First off, Heaney doesn’t translate wanre (dark). In the OE, wanre alliterates with first half-line (weold wideferhð, ruled forever, a reference to God that ends the previous sentence). Since the alliteration doesn’t work in modern English, and since dark night is redundant, Heaney dispenses with it. The line also scans better with one less syllable; the shorter construction heightens the building terror. Sceadugenga is literally, shadow-goer, but shadow-stalker is a neat translation. Since Grendel is on the hunt, it fits the context and it alliterates. There are no adjectives in the OE to match Heaney’s stealthy and swift, but the verb scriðan means to glide, to move silently, so Heaney adds the adjectives to alliterate and to provide the connotation of the OE verb.
As I mentioned, sceotend is literally shooters or archers, but was chosen to alliterate. Heaney’s hall-guards fits the context perfectly. He takes liberties with the next line, however. Line 704 literally reads, who should have guarded the horned-hall (i.e., gabled hall). His slack, asleep at their posts not only provides alliteration, but emphasizes that the guards were not simply asleep, but derelict in their duties. It comes at the cost of losing the description of the hall, but that’s a minor detail that isn’t central.
Heaney also varies the aside that is set off by dashes somewhat. Yldum cuþ is literally known to men, but widely understood carries the same meaning. Scynscaþa is literally phantom-harmer, but fiend works, and the shorter word is needed to make the line scan. Under sceadu is literally, under the shadows, so Heaney’s shadow-bourne is a surprise. It’s a reference Grendel’s mere (bourne or burn is a stream), the place where he Grendel would indeed drag his victims. Bregdan is probably best translated as drag, rather than bear, but then it wouldn’t alliterate with bourne.
The final line is a major alteration. The OE reads literally, but he, keeping watch in enmity for the wrathful one, awaited, enraged, the decision of the battle. Heaney uses one man instead of the OE he, but his choice makes it clear that he’s no longer talking about Grendel. (The Beowulf-poet is not always good about providing clear antecedents.) And he makes bolgenmod, literally enraged or boiling mad, into fighting mood, a nice contextual translation that also succinctly incorporates the sense of in enmity for the wrathful one. Finally, the literal decision of the battle doesn’t carry the sense intended in the OE. Throughout Beowulf, battles and fights are depicted as being decided by God or fate. Beowulf is not awaiting on the sidelines until it’s clear which side will win, rather he must await God’s decision. Heaney’s spoiling for action doesn’t express this connotation either, but it does nicely encapsulate Beowulf’s state of mind.
So Heaney’s translation is artful and reasonably faithful. He does make some changes, but usually there are multiple good reasons behind them.