The grammar of Old English is quite different from that of Modern English, predominantly by being much more inflected. As an old Germanic language, Old English has a morphological system that is similar to that of the Proto-Germanic reconstruction, retaining many of the inflections thought to have been common in Proto-Indo-European and also including constructions characteristic of the Germanic daughter languages such as the umlaut.
Among living languages, Old English morphology most closely resembles that of modern Icelandic, which is among the most conservative of the Germanic languages. To a lesser extent, it resembles modern German.
Nouns, pronouns, adjectives and determiners were fully inflected, with four grammatical cases (nominative, accusative, genitive, dative), and a vestigial instrumental, two grammatical numbers (singular and plural) and three grammatical genders (masculine, feminine, and neuter). First- and second-person personal pronouns also had dual forms for referring to groups of two people, in addition to the usual singular and plural forms. The instrumental case was somewhat rare and occurred only in the masculine and neuter singular. It was often replaced by the dative. Adjectives, pronouns and (sometimes) participles agreed with their corresponding nouns in case, number and gender. Finite verbs agreed with their subjects in person and number.
Nouns came in numerous declensions (with many parallels in Latin, Ancient Greek and Sanskrit). Verbs came in ten main conjugations (seven strong and three weak), all with numerous subtypes, as well as a few additional smaller conjugations and a handful of irregular verbs. The main difference from other ancient Indo-European languages, such as Latin, is that verbs could be conjugated in only two tenses (compared to the six "tenses", really tense/aspect combinations, of Latin), and the absence of a synthetic passive voice, which still existed in Gothic.
Nouns
Old English nouns are grouped by grammatical gender, and inflect based on case and number.
Gender
Old English retains all three genders of Proto-Indo-European: masculine, feminine, and neuter.
Each noun belongs to one of the three genders, while adjectives and determiners take different forms depending on the gender of the noun they describe. The word for "the" or "that" is sē with a masculine noun, sēo with a feminine noun, and þæt with a neuter noun. Adjectives change endings: for instance, since hring ("ring") is masculine and cuppe ("cup") is feminine, a golden ring is gylden hring, while a golden cup is gyldenu cuppe.
In Old English the words for "he" (hē) and "she" (hēo) also mean "it." Hē refers back to masculine nouns, hēo to feminine nouns, reserving the neuter pronoun hit for grammatically neuter nouns. That means even inanimate objects are frequently called "he" or "she." See the following sentence, with the masculine noun snāw:
Compare this parallel sentence, where the neuter noun fȳr (OE equivalent of NE fire) is referred to with hit (OE equivalent of neuter singular nominative NE it):
Only a few nouns referring to people have a grammatical gender that does not match their natural gender, as in the neuter word mæġden ("girl"). In such cases, adjectives and determiners follow grammatical gender, but pronouns follow natural gender: Þæt mæġden sēo þǣr stent, canst þū hīe? ("The girl who [feminine] is standing there, do you know her?").
When two nouns have different genders, adjectives and determiners that refer to them together are inflected neuter: Hlīsa and spēd bēoþ twieċġu ("Fame [masculine] and success [feminine] are double-edged [neuter plural]").
Gender assignment
In Old English (and Indo-European languages generally), each noun's gender derives from morphophonology rather than directly from semantics (word-meaning). In other words, it is not the 'thing' itself that determines the gender of its name (noun), but rather the particular speech-sounds (previously) used to denote that thing's kind (gender). In the ancestor of Old English (namely Proto-Indo-European and later Proto-Germanic), certain speech-sounds in a word-ending generally indicated the word's gender (i.e. kind, sort), but once these word-ending sounds had disappeared from speech over generations, a noun's gender was no longer immediately clear.