In all historical Indo-European languages adjectives possess practically the same morphological features as the nouns, the the sequence of these two parts of speech is an ordinary thing in Indo-European. However, the Nostratic theory (the one which unites Altaic, Uralic, Semitic, Dravidian and Indo-European language families into one Nostratic super-family, once speaking a common Proto-Nostratic language) represented by Illych-Svitych and many other famous linguists, states that adjectives in this Proto-Nostratic tongue were morphologically closer to the verbs than to the nouns.

This theory is quite interesting, because even in Proto-Indo-European, a language which was spoken much later than Proto-Nostratic, there are some proofs of the former predicative function of the adjectives. In other families of the super-family this function is even more clear. In Altaic languages, and also in Korean and Japanese, which are originally Altaic, the adjective plays the part of the predicate, and in Korean, for example, the majority of adjectives are predicative. It means that though they always denote the quality of the noun, they act the same way as verbs which denote action. Adjective "red" is actually translated from Japanese as "to be red", and the sentence Bara-wa utsukusii will mean "the rose is beautiful", while bara is "a rose", -wa is the nominative marker, and utsukusii is "to be beautiful". So no verb here, and the adjective is a predicate. This structure is typical for many Altaic languages, and probably was normal for Proto-Nostratic as well.

The Proto-Indo-European language gives us some stems which are hard to denote whether they used to mean an adjective or a verb. Some later branches reflect such stems as verbs, but other made them adjectives. So it was the Proto-Indo-European epoch where adjectives as the part of speech began to transform from a verbal one to a nominal one. And all Indo-European branches already show the close similarity of the structure of adjectives and nouns in the language. So does the Old English language, where adjective is one of the nominal parts of speech.

As well as the noun, the adjective can be declined in case, gender and number. Moreover, the instrumental case which was discussed before was preserved in adjectives much stronger than in nouns. Adjectives must follow sequence with nouns which they define - thet is why the same adjective can be masculine, neuter and feminine and therefore be declined in two different types: one for masculine and neuter, the other for feminine nouns. The declension is more or less simple, it looks much like the nominal system of declension, though there are several important differences. Interesting to know that one-syllable adjectives ("monosyllabic") have different declension than two-syllable ones ("disyllabic"). See for yourselves:

Strong Declension
 a, ó-stems
     Monosyllabic
                   Sg.
        Masc.     Neut.         Fem.
N blæc (black) blæc        blacu
G blaces          blaces      blæcre
D blacum        blacum      blæcre
A blæcne        blæc         blace
I  blace           blace         -
                   Pl.
N  blace         blacu         blaca
G  blacra        blacra        blacra
D  blacum      blacum      blacum
A  blace         blacu         blaca

Here "I" means that very instrumental case, answering the question (by what? with whom? with the help of what?).

     Disyllabic
        Masc.     Neut.                Fem.
                   Sg.
N  éadig (happy) éadig        éadigu
G  éadiges           éadiges     éadigre
D  éadigum          éadigum   éadigre
A  éadigne           éadig        éadige
I   éadige             éadige
                   Pl.
N  éadige            éadigu      éadiga
G  éadigra           éadigra     éadigra
D  éadigum          éadigum   éadigum
A  éadige            éadigu       éadigu

So not many new endings: for accusative singular we have -ne, and for genitive plural -ra, which cannot be met in the declension of nouns. The difference between monosyllabic and disyllabic is the accusative plural feminine ending -a / -u. That's all.

ja, jó-stems (swéte - sweet)
                 Sg.                                                Pl.
      Masc.      Neut.        Fem.      Masc.     Neut.         Fem.
N  swéte       swéte      swétu     swéte     swétu      swéta
G  swétes      swétes    swétre    swétra    swétra    swétra
D  swétum     swétum   swétre   swétum   swétum  swétum
A  swétne      swéte     swéte     swéte     swétu      swéta
I    swéte       swéte        -

wa, wó-stems
                Sg.
        Masc.         Neut.              Fem.
N  nearu (narrow) nearu           nearu
G  nearwes           nearwes       nearore
D  nearwum          nearwum      nearore
A  nearone            nearu           nearwe
I  nearwe              nearwe
                Pl.
N  nearwe           nearu            nearwa
G  nearora           nearora        nearora
D  nearwum         nearwum     nearwum
A  nearwe            nearu           nearwa

Actually, some can just omit all those examples - the adjectival declension is the same as a whole for all stems, as concerns the strong type. In general, the endings look the following way, with very few varieties (note that "-" means the null ending):
 

Thus if you say "a black tree" that will be blæc tréow (strong), and "a black eye" will sound blace éage. Here is the weak declension example (blaca - black):

         Sg.                                            Pl.
     Masc.       Neut.        Fem.
N  blaca        blace         blace         blacan
G  blacan       blacan       blacan       blæcra
D  blacan       blacan       blacan       blacum
A  blacan       blace         blacan       blacan

Weak declension has a single plural for all genders, which is pleasant for those who don't want to remeber too many forms. In general, the weak declension is much easier.

The suffices we are used to see in Modern English, those -er and -est in weak, weaker, the weakest, are the direct descendants of the Old English ones. At that time they sounded as -ra and -est. See the examples:

earm (poor) - earmra - earmost
blæc (black) - blæcra - blacost

Many adjectives changed the root vowel - another example of the Germanic ablaut:

eald (old) - ieldra - ieldest
strong - strengra - strengest
long - lengra - lengest
geong (young) - gingra - gingest

The most widespread and widely used adjectives always had their degrees formed from another stem, which is called "suppletive" in linguistics. Many of them are still seen in today's English:

gód (good) - betera - betst (or sélra - sélest)
yfel (bad) - wiersa - wierest
micel (much) - mára - máést
lýtel (little) - læ'ssa - læ'st
fear (far) - fierra - fierrest, fyrrest
néah (near) - néarra - níehst, nýhst
æ'r (early) - æ'rra - æ'rest
fore (before) - furþra - fyrest (first)

Now you see what the word "first" means - just the superlative degree from the adjective "before, forward". The same is with níehst from néah (near) which is now "next".

For those who are fond of word composition we can offer some essential materials about the Old English affixation for adjectives:

  1. -ede (group "adjective stem + substantive stem") - micelhéafdede (large-headed)
  2. -ihte (from substantives with mutation) - þirnihte (thorny)
  3. -ig (from substantives with mutation) - hálig (holy), mistig (misty)
  4. -en, -in (with mutation) - gylden (golden), wyllen (wóllen)
  5. -isc (nationality) - Englisc, Welisc, mennisc (human)
  6. -sum (from stems of verbs, adjectives, substantives) - sibbsum (peaceful), híersum (obedient)
  7. -feald (from stems of numerals, adjectives) - þríefeald (threefold)
  8. -full (from abstract substantive stems) - sorgfull (sorrowful)
  9. -léás (from verbal and nominal stems) - slæpléás (sleepless)
  10. -líc (from substantive and adjective stems) - eorþlíc (earthly)
  11. -weard (from adjective, substantive, adverb stems) - inneweard (internal), hámweard (homeward)

The next is the pronoun.
 

            § 5. The Old English Pronoun.

Pronouns were the only part of speech in Old English which preserved the dual number in declension, but only this makes them more archaic than the rest parts of speech. Most of pronouns are declined in numnber, case and gender, in plural the majority have only one form for all genders.

We will touch each group of Old English pronouns and comment on them.

1. Personal pronouns
 

The word for "she" was héo in Old English. The word she probably comes from the feminine demonstrative pronoun séo (see below), which derives from the Common Germanic *sjó. But the exact origin of this simple word is unknown, and there is even a version that it came from Celtic languages (Irish sí [shee]) or from Scandinavian.

All indirect case forms of the pronouns above begin with þ- [th]. It traces back to the Indo-European *t- which became þ in Germanic.

3. Interrogative pronouns

N  hwá      hwæt
G  hwæs    hwæs
D  hwæ'm  hwæ'm
A  hwone   hwæt
I    -           hwý, hwí

Translation is simple. For those who have not guessed yet, hwá means 'who?', hwæt is 'what?'. These pronouns, which actually mean the masculine and the neuter varieties of the same pronoun, derive from Proto-Indo-European *kwis, with *kw becoming hw in Germanic languages. In Gothic the combination hw was considered as one sound which is another proof that the Indo-European the labiovelar sound kw was a single sound with some specific articulation.

Later Germanic languages changed the sound in a different way: in Norwegian it remained as hv, in German turned into w (as in wer 'who', was 'what'), in English finally changed into wh pronounced in most cases [w], but somewhere also like [h] or [hw].

Interesting that the instrumental of the word hwæt, once being a pronoun form, later became the word why in English. So 'why?' is originally an instrumental case of the interrogative pronoun.

Other interrogative pronouns, or adverbs, as they are sometimes called, include the following, all beginning with hw:

hwilc 'which?' - is declined as the strong adjective (see adjectives above)
hwonne 'when?' - this and following are not declined, naturally
hwæ'r 'where?'
hwider 'whither?'
hwonan 'whence?'

4. Other kinds of pronouns

They include definite, indefinite, negative and relative, all typical for Indo-European languages. All of them still exist in Modern English, and all of them are given here:

a) definite
  gehwá (every) - declined the same way as hwá
  gehwilc (each),
  ægþer (either),
  æ'lc (each),
  swilc (such) - all declined like strong adjectives
  sé ylca (the same) - declined like a weak adjective

b) indefinite
  sum (some),
  æ'nig (any) - both behave the same way as strong adjectives

c) negative
  nán, næ'nig (no, none) - declined like strong adjectives

d) relative
  þe (which, that)
  séþe (which, that) - they are not declined

In Proto-Indo-European and in many ancient Indo-European languages there was a special kind of declension calleed pronominal, using only by pronouns and opposed to the one used by nouns, adjectives and numerals. Old English lost it, and its pronouns use all the same endings as the nouns and adjectives. Maybe the only inflection which remembers the Proto-language times, is the neuter nominative -t in hwæt and þæt, the ancient ending for inanimate (inactive) nouns and pronouns.

And now finally some words about the article. In Proto-Indo-European no traces of definite or indefinite articles can be found, and the majority of ancient Indo-European languages lack it either. But still the article is considered a typical "late Indo-European" feature - it started appearing already when languages of the family existed separately. In Homer's Greek language there was no article, not in Mycenaean Greek, but all classical Greek dialects already have the definite article in wide use. Later the difinite article appears in Romance languages (though Latin did not have it at all), Celtic languages (again - Gaulish had no, but all Insular Celtic tongues generated it), in late Germanic (but not in Gothic nor in Old English), and even in several Slavic languages, those which belong to the so-called "Balkan language alliance" (Macedonian, Bulgarian).

Old English did not use the article. It appeared later, coming, as it always happen, for the demonstrative pronoun. But even in this period the texts show us the frequent use of the demonstrative pronoun before nouns in the sentence: ...he heold þæt rice (he held the kingdom). I do not know why it happens and in general why the article appears in the language, I think it could do well without any.

As for the indefinite article, it was a product of the Old English numerals.
 

        § 6. The Old English Numeral.
 
It is obvious that all Indo-European languages have the general trend of transformation from the synthetic (or inflectional) stage to the analytic one. At least for the latest 1,000 years this trend could be observed in all branches of the family.

The level of this analitization process in each single language can be estimated by several features, their presence or absence in the language. One of them is for sure the declension of the numerals.

In Proto-Indo-European all numerals, both cardinal and ordinal, were declined, as they derived on a very ancient stage from nouns or adjectives, originally being a declined part of speech. There are still language groups within the family with decline their numerals: among them, Slavic and Baltic are the most typical samples. They practically did not suffer any influence of the analytic processes. But all other groups seem to have been influenced somehow. Ancient Italic and Hellenic languages left the declension only for the first four cardinal pronouns (from 1 to 4), the same with ancient Celtic.

The Old English language preserves this system of declension only for three numerals. It is therefore much easier to learn, though not for English speakers I guess - Modern English lacks declension at all.

Here is the list of the cardinal numerals:
 

1 án is declined just like a strong adjective, can be only singular, but has masculine, neuter and feminine genders. It is the source of the future indefinite article 'a, an' in Modern English. So 'a house' in fact means "one house", here -n disappeared before a consonant. When at school, many of us thought that 'an' derived from 'a' and it appeares vice versa.

2 twá:
        Masc.    Neut.                  Fem.
N  twegen     tú, twá                 twá
G                twégea, twégra
D                twæ'm, twám
A  twegen     tú, twá                 twá

So the genders have differences only in nominative and accusative cases, and indirect cases (genitive and dative) have common forms for all three genders. No number can be changed for it, and originally this numeral was dual, which seems natural.

3 þríe:
      Masc.               Neut.              Fem.
N  þríe, þrí, þrý   þrío, þréo       þrío, þréo
G                        þríora, þréora
D                        þrím
A  þríe, þrí, þrý   þrío, þréo       þrío, þréo

A typical i-stem noun. Strange is the following: while in the case of "two" the Modern English lost masculine and neuter forms and picked up the feminine one for use ('two' < twá), here we have another case, when the feminine and neuter were forgotten, and today's three comes directly from the masculine þríe.

And the last is the numeral begen, bú, bá (both) which is declined the same way as twá and is also dual.

Ordinal numerals  use the suffix -ta or -þa, etymologically a common Indo-European one (*-to-).
 

Mainly according to Old English texts ordinal numerals were used with the demonstrative pronoun þá before them. This is where the definite article in 'the first', 'the third' comes from. To say "the 22nd", for example, you should combine the following: either twá and twenigoþa (two and twentieth), or óþer éac twentigum (second with twenty). So the order is different from the modern English, but instead closer to Modern German where "the 22nd" sounds like zwei und zwanzig (two and twenty).

At all, it is easy to notice that the words in English became much shorter, and therefore simpler in pronunciation and learning. It is much easier to pronounce "hundredth" than hundtéontiogoþa, "fourth" than féowertéoþa. Modetrn English acquired words mainly having one or two syllables, but this was not the rule in the Old English period.
 

        § 7. The Old English Adverb.

Just some words about the adverbs.

They can be either primary (original adverbs) or derive from the adjectives. In fact, adverbs appeared in the language rather late, and eraly Proto-Indo-European did not use them, but later some auxiliary nouns and pronouns losing their declension started to play the role of adverbial modifiers. That's how thew primary adverbs emerged.

In Old English the basic primary adverbs were the following ones:
þa (then)
þonne (then)
þæ'r (there)
þider (thither)
nú (now)
hér (here)
hider (hither)
heonan (hence)
sóna (soon)
oft (often)
eft (again)
swá (so)
hwílum (sometimes).

Secondary adverbs originated from the instrumental singular of the neuter adjectives of strong declension. They all add the suffix -e: wide (widely), déope (deeply), fæste (fast), hearde (hard). Another major sugroup of them used the suffixes -líc, -líce from more complexed adjectives: bealdlíce (boldly), freondlíce (in a friendly way).

Adverbs, as well as adjectives, had their degrees of comparison:

wíde - wídor - wídost (widely - more widely - most widely)
long - leng (long - longer)
feorr (far) - fierr
sófte (softly) - séft
éaþe (easily) - íeþ
wel (well) - betre - best
yfele (badly) - wiers, wyrs - wierst
micele (much) - máre - mæ'st