The Proto-Germanic and the old Germanic languages were synthetic languages (the relationships between the parts of the sentence were shown by the forms of the words rather than position in the sentence or by auxiliary words). One the main processes in the development of the Germanic morphological system was the change in the word structure. The common I-E notional word consisted of 3 elements: root (expressing the lexical meaning), inflexion (ending) (showing the grammatical form), stem-forming suffix. However in Germanic languages the stem-forming suffix fuses with the ending and is often no longer visible.
The Germanic nouns had a well-developed case system with 4 cases: nominative, genitive, dative, accusative. And two number forms: singular and plural. They also had the category of gender: feminine, masculine, neuter.
Germanic adjectives had two types of declination: weak and strong. They also had degrees of comparison.
Germanic verbs are divided into 2 principal groups: strong and weak. Depending on the way they formed their past tense forms. The past tense of strong verbs was formed with the help of ablaut(÷åðåäîâàíèå ãëàñíûõ). Weak verbs expressed past tense with the help of the dental suffix “d/t”. The Germanic verb had a well-developed system of categories including the category of person 1st, 2nd, 3rd; category of number singular/plural. Also Germanic verb had tense: past and present. They also had mood: indicative, imperative, optative.
The grammatical forms of the word were built by means of suppletion (îáðàçîâàíèå ôîðì îäíîãî è òîãî æå ñëîâà îò ðàçíûõ êîðíåé) (the usage of two or more different roots as forms of one and the same word) (I, my, mine, me) (ich, mich, mir).
Inflections.
Though in the Germanic languages inflections were simpler and shorter than in other in other I-E languages. Sound interchange. The usage of interchange of vowels and consonants for the purpose of word and form building. (tooth-teeth, build-built).
Ablaut or vowel gradation. An independent vowel interchange unconnected with any phonetic conditions used to differentiate between grammatical forms of one and the same word. The Germanic ablaut was consistently used in building the principal forms of strong verbs.