Old English is a language closely related to Old Frisian, both forming part of the West Germanic branch of the Germanic languages, a sub-group of the Indo-European language family.
The Proto-Indo-Europeans were the speakers of the Proto-Indo-European language (PIE). Knowledge of them comes chiefly from linguistic reconstruction. According to some archaeologists, PIE speakers cannot be assumed to have been a single, identifiable people or tribe, but were a group of loosely related populations ancestral to the later, still partially prehistoric, Bronze Age Indo-Europeans. However, this view is not shared by linguists, as proto-languages generally occupy small geographical areas over a very limited time span, and are generally spoken by close-knit communities such as a single small tribe.
The following changes are known or presumed to have occurred in the history of Proto-Germanic in the wider sense from the end of Proto-Indo-European up to the point that Proto-Germanic began to break into mutually unintelligible dialects.
Pre-Proto-Germanic: This stage began with the separation of a distinct speech, perhaps while still forming part of the Proto-Indo-European dialect continuum.
Early Proto-Germanic: This stage began its evolution as a form of centum PIE that had lost its laryngeals and had five long and six short vowels, as well as one or two overlong vowels. The consonant system was still that of PIE minus palatovelars and laryngeals, but the loss of syllabic resonants already made the language markedly different from PIE proper.
Late Proto-Germanic: By this stage, Germanic had emerged as a distinctive branch and had undergone many of the sound changes that would make its later descendants recognisable as Germanic languages. It had shifted its consonant inventory from a system rich in plosives to one containing primarily fricatives, had lost the PIE mobile pitch accent in favour of a predictable stress accent, and had merged two of its vowels. The stress accent had also begun to cause the erosion of unstressed syllables already, which would continue in its descendants up to the present day. This final stage of the language included the remaining development until the breakup into dialects, and most notably featured the appearance of nasal vowels and the first beginning of umlaut, another characteristic Germanic feature.
Old English is much closer to modern German and Icelandic than modern English in most respects, including its grammar. It is fully inflected with five grammatical cases (nominative, accusative, genitive, dative, and instrumental), two grammatical numbers (singular and plural) and three grammatical genders (masculine, feminine, and neuter). First and second person personal pronouns also have dual forms for referring to groups of two people. Adjectives, pronouns and (sometimes) participles agree with their antecedent nouns in case, number and gender. Finite verbs agree with their subject in person and number.
Nouns come in numerous declensions. Verbs come in nine main conjugations (seven strong and two weak), each with numerous subtypes, as well as a few additional smaller conjugations and a handful of irregular verbs. The main difference from other Indo-European languages, such as Latin, is that verbs can be conjugated in only two tenses and have no synthetic passive voice.
Gender in nouns are grammatical, as opposed to the natural gender that prevails in modern English. That is, the grammatical gender of a given noun does not necessarily correspond to its natural gender, even for nouns referring to people. For example, sēo sunne (the Sun) is feminine, se mōna (the Moon) is masculine, and þat wīf "the woman/wife" is neuter (compare German cognates die Sonne, der Mond, das Weib). Pronominal usage could reflect either natural or grammatical gender, when it conflicts.
The history of Old English can be subdivided in:
Prehistoric Old English (c. 450 to 650); for this period, Old English is mostly a reconstructed language as no literary witnesses survive (with the exception of limited epigraphic evidence).
Early Old English (ca. 650 to 900), the period of the oldest manuscript traditions, with authors such as Cædmon, Bede, Cynewulf and Aldhelm.
Late Old English (c. 900 to 1066), the final stage of the language leading up to the Norman conquest of England and the subsequent transition to Early Middle English.