I've been attempting for a few weeks now to unlock the exact nature of Bill Callahan's Apocalypse. It remains elusive; certainly, he appears to be using the phrase to mean a revelation or epiphany of some kind, both life-changing and extremely personal, and it's without doubt that there is a story being told here, a narrative that runs through the album like a novel, albeit one that is distinctly oblique and cryptic. But interpretations by listener or critic remain just that; assumptions, guesswork. From the inside, the subject matter may be very specific; from the outside, it's impressionistic, a mood piece. A disquieting, suggestive panorama of dusty American Gothic, the album hints at a wider world of darkness and abandonment, but remains ultimately closed-in and private. There is enough light here to make out the shadowy shapes of things, but little more.

His 14th proper album and his third since ditching the Smog moniker, Apocalypse is mostly spare and understated. Callahan remains a master of tension and dynamics within a deliberately limited palette: the insistent strum of 'The Drover' is tinged with fiddle and the odd fleck of distorted feedback, perfectly conjuring the atmosphere of this strange, Existentialist Western fable, in which herding cattle seems to be a metaphor for writing songs, and when the cattle suddenly turn against him, "I am a drover doublefold". On the barely-sketched yet perfectly weighted vignette of love and loss, 'Baby's Breath,' the guitar repeatedly speeds up to double-time, then slows back down to a dragging pick again, the musical accompaniment serving and reflecting the narrative, as in a film.

Throughout, the contrast between Callahan's resolutely deadpan, un-funky vocal style and the grooves gradually building behind him is compulsive, and sometimes comic. 'America!' in particular takes up immediate residency on your internal ipod, with an almost Can or Monks-like level of simplistic repetition. The album's most instantly catchy track, 'America!' starts out as a rusty one-chord strut, almost like some club-footed approximation of reggae, dragging its weight behind it, but then becomes increasingly layered, multi-rhythmic and aggressive as it goes on. Lyrically, it's ambiguous: Bill's musings on his homeland seem distinctly non-committal, and when he does make a statement it's hard to tell whether it's heartfelt or ironic. Name-checking assorted country singers by the rank they attained in the forces, his exact point is never clear, even when he confesses, in apparently throwaway fashion and almost as though it's only just occurred to him, "I never served my country." The blank gaze of both words and music reflect the listeners' own assumptions back at them: is it fanciful to interpret the wild, distorted electric guitar singing over the top line as a nod to Hendrix's take on the 'Star-Spangled Banner', or to be reminded of Ginsberg's 1956 poem of the same name in the stream-of-consciousness feel of the lyrical observations? Probably, but I think I'm on firmer ground in suggesting that the song has been deliberately and artfully constructed in such a way as to leave space for such associations to arise.

In a recent interview with the New York Times, Callahan told writer Ben Ratliff how a seemingly casual aside in the song 'Universal Applicant' is in fact the fulcrum of the whole record: how when Callahan sings of firing off a flare gun, and then actually makes the soft, sibilant sound of the gun's report, that from that point on the whole record is illuminated: the narrative becomes clearer and more direct. And to some extent this seems true, although the level of illumination is relative: it's not exactly broad daylight. But the record does seem to shift gear around this halfway mark, and for all that it retains a certain dirt-track minimalism, the album that the second half of Apocalypse keeps reminding me of is one of the most lushly produced in the rock canon: Van Morrison's Astral Weeks¬.

Like Morrison, Callahan draws on traditional musical forms but takes them somewhere else, partly through a modernist, literary approach to song construction. Both often appear to be rambling, following a train of thought in their lyrics until they hit upon an image of diamond clarity or a lyric of devastating personal intensity, and in both cases you suspect that the apparently freeform delivery conceals a meticulous sense of structure and ruthless editing.

Musically, the comparison is suggested by the jazzy, flute-assisted backing of 'Universal Applicant' itself, and even more so by the summer morning funk of 'Free's.' The latter is in some ways a mirror image of the earlier 'America!', not only because of the unconventional use of punctuation in both titles, but because both consider questions of nationality and identity, liberty and duty. "Free's" are essentially Americans, or the citizens of liberal Western democracies- those who "belong to the free," i.e. 'The Free World.' The spirit of Astral Weeks is there too in the gorgeous, shuffling rhythms of 'Riding for the Feeling,' which suggest a soulful break-up song, but in fact this seems to be about a day doing interviews: Callahan promoting his record to a stream of eager journalists, all filing up to his anonymous hotel room and wanting to know just what the album's about, but he can't tell them. Too late, he realises he was just "riding for the feeling." Again like Morrison, Callahan seems to have an innate distrust of any attempts to explain or interpret the creative process. And maybe "Riding for the Feeling" is as much the 'meaning' of Apocalypse as anything else.

As for Callahan's personal moment of revelation, that seems to be described on the album's final track, 'One Fine Morning,' which comes perhaps closest of anything here to the Celtic country-soul-jazz of Astral Weeks and 'TB Sheets.' Stunning and yet under-stated, this grand finale is in some ways delivered almost as an afterthought: "One fine morning… yeah, it's all coming back to me now… my apocalypse… my apocalypse," Callahan speak-sings, before describing how "the curtains rose and burned in the morning sun." The conversational, improvised-sounding recitation, all tension and release, holding back, is very much in the Van Morrison style. "I said hey, no more drovering," he concludes, referring back to the opening track, bringing us full circle; he then ends by singing the album's catalogue number, twice over, which I can only interpret as a kind of Brechtian distancing technique, reminding us that we are only listening to a record, something separate from his real feelings and real life.

Perhaps, in fact, the apocalypse described is something as banal as Callahan deciding to spend more time with his family, and less time on the road; in the end, it doesn't matter. What matters is the art that he's created from his experience, the feeling successfully conveyed. Apocalypse is a mystery that will continue to haunt you through moments yet to come.