A fourteenth-century reader would likely have an easier time than you or I jumping right into an Old English text, but would by no means have found it straightforward. Their primary advantage would be lexical; there are all sorts of common Old English words that still had currency in Middle English (like sitthe, OE siððan = since/after) which have now dropped out of Modern English.
But the language had changed in lots of other ways that would have presented barriers. Middle English has a far less heavily inflected language than OE. Grammatical inflection involves the changing of the forms of words (morphology) based on grammatical case. In Old English there are four such cases – nominative (the subject), accusative (the object), genitive (possessive) and dative (with/from etc.) – as well as plural forms. You can think of these in terms of our pronouns, which are still inflected. I (nom.) do the verb; the verb is done to me (acc.); those are my (gen.) nouns; etc. This is a (simplified!) chart for OE. In OE, nouns, adjectives and pronouns are all inflected. You’ll also notice the mess of verb endings. This had simplified a little by the fourteenth century (think of the cliché distinction between ‘-est/-eth’ in “Ye Olde English” parody speech), and (as far as I know?) the ‘-don’ past plural ending had largely dropped out of usage.
Other significant changes had occurred. Norse influence had shaken up the pronouns; the OE female 3rd-person ‘heo’ had made way for the snazzy new ME ‘she’. The plural forms ‘they/them/their' had also made inroads, although not universally. This was all good stuff, as Old English pronouns are quite homogenous and can be confusing. Some vowels had moved around, though this probably wouldn’t have posed too much trouble in reading. All in all, by the fourteenth century there would have been significant linguistic barriers to reading Old English, especially in complex texts like the poetry, which alliterates heavily and so often draws on a corpus of arcane formal diction.
It’s worth considering the difficulty that obtaining and reading the books themselves would have presented. Unless you had access to a library, particularly an old monastic library, you probably wouldn’t find them just lying around. Collecting enough to “learn” Old English in any meaningful sense would have presented no small challenge to your average fourteenth-century reader. And what you found when you obtained such a book might not even be legible to your eyes. Here’s British Library Cotton MS Vitellius A XV, the Beowulf manuscript (I’ve put you at 132r, the start of the poem), copied c.1000. Compare it to some of the later medieval hands on this page, which has set and cursive examples from the thirteenth through fifteenth centuries. A lot had changed! The forms of s, r and g had altered in ways that might temporarily vex a later medieval reader, and the letters æ (ash) ð (eth) and ƿ (wynn) had dropped out entirely. We have the luxury of our neatly typed modern editions of Old English texts; medieval readers had to make do with manuscripts that were obscured by changes in language/handwriting and were, in all likelihood, damaged by time.
That said, we do know that some Old English books were treated with what one might call antiquarian interest in the later Middle Ages. By the fifteenth century the library of Bury St Edmunds contained (at least) a copy of Ælfric’s homilies and an Old English rule of St Benedict. A copy of the West Saxon Gospels that had found its way from Kent to Tewkesbury (Yale University, Beinecke 578) was rebound in the early fourteenth century and still survives in that binding. An old binding strip in BodL MS Junius 11, which contains the Old English Genesis A/B, Exodus, Daniel and Christ and Satan poems, dates from the late thirteenth or early fourteenth century. The so-called “Tremulous Hand of Worcester” provided a considerable number of glosses to a number of Old English manuscripts at Worcester in the thirteenth century.
All of this suggests that Old English manuscripts were at least being actively preserved in the fourteenth century, and perhaps being read by a learned few with the access, the interest, the time and the brains to get to grips with the language (chiefly, I would guess, monks). The fullest example of fourteenth-century engagement with Old English is in BodL Tanner 10, a copy of Bede’s Historia Ecclesiastica copied in the first half of the tenth century. It contains some 119 annotations and interlinear glosses in a fourteenth-century hand/s. On line 8 of the linked image (f. 3v), for instance, you’ll notice that forhogodon (despised) is glossed in Latin sp(er)nendo. Dating such small amounts of text in such tiny handwriting is never easy, but the s and d are, for instance, dead giveaways and this date is the scholarly consensus.
Whoever wrote these glosses does seem to have been able to read most of the book; one assumes they only glossed words that they found difficult. It’s worth knowing that about 75% of the book’s Latin glosses are simply from Bede’s widely available Latin original, which the reader (readers?) was no doubt able to consult to aid their reading/translation. I’m not really qualified to say whether the sum total of the reader’s glosses means that they could meaningfully read Old English. Sharon Rowley’s opinion is that it is a definite possibility. The scope of such an ability in the fourteenth century is even harder to quantify, and here I defer to Richard Gameson, who says of the Tanner Bede that ‘intelligent interest in an Old English text is rare at this date’. Seth Lerer’s survey of the post-Conquest survival of Old English scarcely mentions the fourteenth century at all.
Sources:
Simon Horobin and Jeremy Smith, An Introduction to Middle English (2002).
Roy Michael Liuzza, ‘The Yale fragments of the West Saxon gospels’, Anglo-Saxon England 17 (1988), 67–82.
Barbara Raw, ‘The Construction of Oxford, Bodleian Library, Junius 11’, in Anglo-Saxon Manuscripts: Basic Readings, ed. Mary P. Richards (2001), 251–76.
Sharon M. Rowley, The Old English Version of Bede’s Historia Ecclesiastica, (2011).
Richard Gameson, ‘The Fabric of the Tanner Bede’, Bodleian Library Record 14 (1992), 176–206.
Seth Lerer, ‘Old English and its afterlife’, The Cambridge History of Medieval English Literature, ed. David Wallace (1999), 7–34.
Excellent question!
There are a few things to unpack here. First, Chaucer wrote primarily in the London accent, which became the king's English, therefore the prestigious form that gets standardised and subsequent forms of standard language are derived from it. He did incorporate the dialectal variations of the country in his writing in order to put more flavour into the respective characters. The knight uses more French-derived words than the guy from the north of England, who uses more words originating in Old Norse.
Bough and Cable in their A History of the English Language talk about how the Middle English period is characteristic for its diverse dialectal representation in the writings that survive from the period. The manuscripts from the northeast of the country stick very largely to the Germanic roots while the case system is almost completely gone at a time when in the southwest England you still have the old personal pronouns ("heo" or "hio" for "she", "hi" or "hie" for "they") and remnants of the case system. The south also has a larger presence of French loanwords.
Also, we can see differences in the way poetry is being composed. Chaucer writes in rhyme, but contemporary to him, poems like Sir Gawain and the Green Knight preserve the Old English alliterative style and Germanic vocabulary, with loans from Old Norse. The langauge wasn't evolving at the same pace in every part of the country and some changes were faster in the northeast than in the rest of the country. Spelling wasn't standardised because people spellt the way they spoke, so it reflected the local dialect much more closely than now.
The second thing to unpack is Old English and its transition into Middle English. Our current division of the language stages into Old, Middle, and Modern comes from the 19th century scholar Henry Sweet. He based the stages in part on the system of case levelling and then disappearance. So Old English, in his view, had nice and neat diversity in case endings. Middle English had levelled inflections (which means that all the diverse case endings were becoming reduced to -on, -en, -an), while Modern English has absent case inflections. Middle English also has a huge influx of loanword from Old Norse and Old French. However, this is too neat of a division and too simplistic.
Barbara Strang in her A History of English separated the stages of the evolution of the English language into 200-year periods, which I think corresponds to the gradual evolution much better. Most scholars would date the beginning of Middle English to either 1100 or 1150, but we all know that these are just dubious dates and you can't label language development like this, as I'll show next. Based on Strang, there are two stages of transition within Middle English. Years 970-1170 and between 1170-1370. The first period is very characteristic of two things that are closely related - levelling and collapse of the case system in many parts of the country and therefore the word order starts to resemble the modern one with greater use of prepositions to indicate a word's grammatical function in a sentence. The second stage is characteristic of the vast number of loanwords that enter the language with the case system collapse finalising.
Pretty much everyone studying this area agrees that the collapse of the levelling of inflections probably started decades before we see it in our manuscripts for the first time (the theory being that the prestigious West-Saxon dialect was evolving into a standard written form because of the House of Wessex unifying England, therefore it was the King's English and standardised language sponsored by kings is resistant to changes in the spoken form). This is the first stage in transition from OE to MidE - 970-1170. The poem The Battle of Maldon, written around the year 1000, has several instances of case ending levelling, but it's inconsistent in the usage of it (dative plural ends with both the original -um or the levelled -on in different parts of the text), which means that the spoken form had already had levelled inflections for maybe 20-30 years or more. The only surviving manuscript for Beowulf is from around the year 1000 (look at Klaeber's Beowulf 4th Ed.) and it has a few words that have levelled inflections too, but not many (which gives more credence to its age due to the conservative case endings and thus it's very likely copied from an older manuscript from an earlier era).
However, not even Henry Sweet would date the beginning of Middle English to this period, long before the Conquest. There is actually less change in the language between The Battle of Maldon and the Peterborough manuscript of the Anglo-Saxon Chronicle account for the year 1100. The only major thing that happens is the increased levelling of the case endings. Bigger change happens between the accounts for the years 1100 and 1154. In the account for 1154, dative and accusative are assimilated into each other, word order is very similar to Modern English, though some compositional traits of Old English are still there (and some of its flexibility too). But in this account we already have some French words creeping in (court, procession, etc.).
We know that at this time, people would still be able to understand Beowulf or any other OE writings, the language hadn't undergone as much change yet. In fact, many of our surviving texts of Old English (meaning copied rather than composed) are from the late 12th century, perhaps even from the reign of Richard the Lionheart and John Lackland. Not only were old texts copied and preserved, but new were composed, like Ormulum. But once French words enter the language in droves, or even Old Norse words, when the personal pronouns change (for example from OE "hie" to the ON "they"), it's gonna be increasingly difficult to wrap your head around OE texts.
By the 14th century, it really depends on the part of the country you're from. The transition from OE to MidE happens at different pace in different parts of the country. Southwest keeps the case system for longer, but uses more French loans, while the northeast is using a lot of Old Norse loans alongside OE originals, but the case system is completely gone already. Maybe in the former Danelaw or Nothumbria, you would be able to understand more of Beowulf because of the vocabulary, but your grammar would be very stripped and simplified compared to the poem. But someone from Wessex could perhaps understand different parts of the text and they would have understood the sentence structure better because of the levelled use of case endings they still might have had, which is still better than not having the case system at all while trying to understand the text.
Can you link me to your middle english reading? I'd like to try it