The pronunciation of Old English words commonly differs somewhat from that of their modern equivalents. The long vowels in particular have undergone considerable modification. Thus the Old English word stan is the same word as Modern English stone, but the vowel is different. Words like heafod (head), fæger (fair), or sawol (soul) show forms that have been contracted in later English. All of these cases represent genuine differences of pronunciation.
The a sound has shifted to the sound of o in Modern English. Other vowels have also undergone changes, e.g.
fōt (Old English ) —— foot (Modern English)
cēne (Old English ) —— keen (Modern English)
hū (Old English ) —— how (Modern English)
However, some of the first look of strangeness that Old English has to the modern reader is due simply to differences of spelling. Old English made use of two characters to represent the sound of th: þ and ð, thorn and eth, respectively, as in the word wiþ (with) or ða (then), which we no longer employ.
Old English represented the sound of th by p and ð as in the word wiρ (O. E.) —— with (Mod. E.), and the word ðā (O. E.) —— then (Mod. E.), the sound of sh by sc as in scēap (O. E.) —— sheep (Mod. E.) or scēotan (O. E.) —— shoot (Mod. E.), and the sound of k by c as in cynn (O. E.) —— kin (Mod. E.) or nacod (O. E.) —— naked (Mod. E.).
The vocabulary of Old English consisted mainly of Anglo-Saxon words. But when the Norman Conquest in 1066 brought French to England much of the English vocabulary was replaced by words borrowed from French and Latin. If we open any Old English dictionary, we find that about 85 percent of the Old English vocabulary was no longer in use during this period. Of course, the basic elements of the vocabulary have remained. They express fundamental concepts of human life, such as: mann (man); wīf (wife), cild (child), hūs (house), bern (bench), mete (meat , food) , gærs (grass), lēaf (leaf) , fugol (fowl, bird), gōd (good), hēah (high), strang (strong), etan (eat), drincan ( drink ), slæpan (sleep ), libban (live ) . feohtan (fight), etc.
Old English was a highly inflected language. It had a complete system of declensions with four cases and conjugations. So Old English grammar differs from Modern English grammar in declensions and conjugations.
There are two classes of languages in the world: synthetic and analytic. A synthetic language is one which shows the relation of words in a sentence largely by means of inflections. An analytic language is one which indicates the relation of words in a sentence by means of word order, prepositions or auxiliary verbs, rather than by inflections.
Old English is a synthetic language. Old English nouns and adjectives have four cases: the nominative case, the genitive case, the dative case and the accusative case. Apart from these four cases, Latin nouns have the ablative and the locative cases. That is to say, Latin nouns have six cases just like Modern Russian nouns.
Take a Latin sentence for example.
The sentence “Nero interfecit Agrippinam.” (Nero killed Agrippina.) has the same meaning as the sentence “Agrippinam interfecit Nero.” This is because the word Nero is in the nominative case, and the word Agrippinain is in the accusative case. Therefore no matter where these words stand, they express the same meaning.
In Modern English, a noun used as a subject and object does not have different forms. There remain today only two case forms: those of the nominative case and the possessive case: man, man’s. Modern English depends upon word order to show the relation of words in a sentence. Different word order may result in different meaning. The sentence “Nero killed Agrippina.” is completely opposite to the sentence “Agrippina killed Nero.” in meaning.
A History of the English Language. Baugh, Albert C., and Thomas Cable. 4th ed. Englewood Cliffs, New Jersey: Prentice Hall, 1993.