Neither identified sources nor analogues for Beowulf can be definitively proven, but many conjectures have been made. These are important in helping historians understand the Beowulf manuscript, as possible source-texts or influences would suggest time-frames of composition, geographic boundaries within which it could be composed, or range (both spatial and temporal) of influence (i.e. when it was "popular" and where its "popularity" took it). There are five main categories in which potential sources and/or analogues are included: Scandinavian parallels, classical sources, Irish sources and analogues, ecclesiastical sources, and echoes in other Old English texts.
Early studies into Scandinavian sources and analogues proposed that Beowulf was a translation of an original Scandinavian work, but this idea has been discarded. In 1878, Guðbrandur Vigfússon made the connection between Beowulf and the Grettis saga. This is currently one of the few Scandinavian analogues to receive a general consensus of potential connection. Tales concerning the Skjöldungs, possibly originating as early as the 6th century were later used as a narrative basis in such texts as Gesta Danorum by Saxo Grammaticus and Hrólfs saga kraka. Some scholars see Beowulf as a product of these early tales along with Gesta Danorum and Hrólfs saga kraka, and some early scholars of the poem proposed that the latter saga and Beowulf share a common legendary ancestry, Beowulf 's Hrothulf being identified with Hrólf Kraki ancestry. Paul Beekman Taylor argued that the Ynglingasaga was proof that the Beowulf poet was likewise working from Germanic tradition.
Friedrich Panzer attempted to contextualise Beowulf and other Scandinavian works, including Grettis saga, under the international folktale type 301B, or "The Bear's Son" tale. However, although this folkloristic approach was seen as a step in the right direction, "The Bear's Son" tale was seen as too universal. In a term coined by Peter Jørgensen (the "two-troll tradition"), a more concise frame of reference was found. The "two-troll tradition" refers to "a Norse 'ecotype' in which a hero enters a cave and kills two giants, usually of different sexes." Both Grettis saga and Beowulf fit this folktale type.
Scholars who favored Irish parallels directly spoke out against pro-Scandinavian theories, citing them as unjustified. Wilhelm Grimm is noted to be the first person to link Beowulf with Irish folklore. Max Deutschbein, however, the first person to present the argument in academic form. He suggested the Irish Feast of Bricriu as a source for Beowulf—a theory that was soon denied by Oscar Olson. Swedish folklorist Carl Wilhelm Von Sydow argued against both Scandinavian translation and source material due to his theory that Beowulf is fundamentally Christian and written at a time when any Norse tale would have most likely been pagan.
In the late 1920s, Heinzer Dehmer suggested Beowulf as contextually based in the folktale type "The Hand and the Child," due to the motif of the "monstrous arm"—a motif that distances Grettis saga and Beowulf and further aligns Beowulf with Irish parallelism. James Carney and Martin Puhvel also agree with this "Hand and the Child" contextualisation. Carney also ties Beowulf to Irish literature through the Táin Bó Fráech story. Puhvel supported the "Hand and the Child" theory through such motifs as "the more powerful giant mother, the mysterious light in the cave, the melting of the sword in blood, the phenomenon of battle rage, swimming prowess, combat with water monsters, underwater adventures, and the bear-hug style of wrestling."
Attempts to find classical or Late Latin influence or analogue in Beowulf are almost exclusively linked with Homer's Odyssey or Virgil's Aeneid. In 1926, Albert S. Cook suggested a Homeric connection due to equivalent formulas, metonymies, and analogous voyages. James A. Work's essay "Odyssean Influence on the Beowulf" also supported the Homeric influence. He stated that encounter between Beowulf and Unferth was parallel to the encounter between Odysseus and Euryalus in Books 7–8 of the Odyssey even to the point of them both giving the hero the same gift of a sword upon being proven wrong in their initial assessment of the hero's prowess. This theory of Homer's influence on Beowulf remained very prevalent in the 1920s, but started to die out in the following decade when a handful of critics stated that the two works were merely "comparative literature" although Greek was known in contemporary England. Bede states that Theodore, a Greek, was appointed Archbishop of Canterbury in 668, and he taught Greek. Several English scholars and churchmen are described by Bede as being fluent in Greek due to being taught by him; Bede claims to be fluent in Greek himself.
Friedrich Klaeber somewhat led the attempt to connect Beowulf and Virgil near the start of the 20th century, claiming that the very act of writing a secular epic in a Germanic world is contingent on Virgil. Virgil was seen as the pinnacle of Latin literature, and Latin was the dominant literary language of England at the time, therefore making Virgilian influence highly likely. Similarly, in 1971, Alistair Campbell stated that the apologue technique used in Beowulf is so infrequent in the epic tradition aside from when Virgil uses it that the poet who composed Beowulf could not have written the poem in such a manner without first coming across Virgil's writings.
Whether seen as a pagan work with "Christian colouring" added by scribes or as a "Christian historical novel, with selected bits of paganism deliberately laid on as 'local colour'," as Margaret E. Goldsmith did in 'The Christian Theme of Beowulf,;" it cannot be denied that Biblical parallels occur in the text. Beowulf channels Genesis, Exodus, and Daniel in its inclusion of references to God's creation of the universe, the story of Cain, Noah and the flood, devils or the Devil, Hell, and the Last Judgment.
The poem mixes the West Saxon and Anglian dialects of Old English, though it predominantly uses West Saxon, as do other Old English poems copied at the time.
There is a wide array of linguistic forms in the Beowulf manuscript. It is this fact that leads some scholars to believe that Beowulf has endured a long and complicated transmission through all the main dialect areas. The poem retains a complicated mix of the following dialectical forms: Mercian, Northumbrian, Early West Saxon, Kentish and Late West Saxon. Kiernan argues that it is virtually impossible that there could have been a process of transmission which could have sustained the complicated mix of forms from dialect to dialect, from generation to generation, and from scribe to scribe.
Kiernan's argument against an early dating based on a mixture of forms is long and involved, but he concludes that the mixture of forms points to a comparatively straightforward history of the written text as:
...an 11th-century MS; an 11th-century Mercian poet using an archaic poetic dialect; and 11th-century standard literary dialect that contained early and late, cross-dialectical forms, and admitted spelling variations; and (perhaps) two 11th-century scribes following slightly different spelling practices.
According to this view, Beowulf can largely be seen to be the product of antiquarian interests and that it tells readers more about "an 11th-century Anglo-Saxon's notions about Denmark, and its pre-history, than it does about the age of Bede and a 7th- or 8th-century Anglo-Saxon's notions about his ancestors' homeland." There are in Beowulf rather more than thirty-one hundred distinct words, and almost thirteen hundred occur exclusively, or almost exclusively, in this poem and in the other poetical texts. Considerably more than one-third of the total vocabulary is alien from ordinary prose use. There are in round numbers three hundred and sixty uncompounded verbs in Beowulf, and forty of them are poetical words in the sense that they are unrecorded or rare in the existing prose writings. One hundred and fifty more occur with the prefix ge- (reckoning a few found only in the past-participle), but of these one hundred occur also as simple verbs, and the prefix is employed to render a shade of meaning which was perfectly known and thoroughly familiar except in the latest Anglo-Saxon period. The nouns number sixteen hundred. Seven hundred of them, including those formed with prefixes, of which fifty (or considerably more than half) have ge-, are simple nouns. at the highest reckoning not more than one-fourth is absent in prose. That this is due in some degree to accident is clear from the character of the words, and from the fact that several reappear and are common after the Norman Conquest.