Like most Indo-European languages, Greek is highly inflected. Greek grammar has come down through the ages fairly intact, though with some simplifications. For example Modern Greek features two numbers: singular and plural. The useless but sublime dual of Ancient times was abandoned at a very early stage. The instrumental case of Mycenaean Greek disappeared in the Archaic period, and the dative-locative of Ancient Greek disappeared in the late Hellenistic. The remaining cases (nominative, accusative, genitive and vocative) remain intact. The three ancient gender noun categories (masculine, feminine and neuter) never fell out of use, while adjectives agree in gender number and case with their respective nouns, as do their articles. Greek verbs are inflected for:
* mood - indicative, subjunctive, imperative - but the ancient optative was lost.
* aspect - perfective, stative, imperfective
* voice - active, mediopassive (reflexive, middle and passive)
* tense - present, past, future
* person - first, second, third, singular and plural (and originally dual).
Due to the language's flexibility in forming compounds and derived words, the infinitive of verbs was gradually and successfully replaced by a periphrastic subjunctive and derived nouns.
A great syntactical reformation took place during Hellenistic times, resulting in many similarities between late Koine and Modern Greek. However since Greek syntactical relations are expressed by means of case endings, Greek word order has always been relatively free. In Attic Greek the availability of the definite article and the infinitive and participle clauses permit the construction of very long, complex yet clear sentences. This technique of Attic prose (known as periodic style) is unmatched in other languages. Since Hellenistic times Greek tended to be more periphrastic, but much of the syntactical and expressive power of the language were preserved.
Greek is a language distinguished by an extraordinarily rich vocabulary. In respect to the roots of words, ancient Greek vocabulary was essentially of Indo-European origin, but with a significant number of borrowings from the idioms of the populations that inhabited Greece before the arrival of the Proto-Greeks. Words of non-Indo-European origin can be traced into Greek from as early as Mycenaean times; those include a large number of Greek toponyms. The vast majority of Modern Greek vocabulary is directly inherited from ancient Greek, although in certain cases words have changed meanings. Words of foreign origin have entered the language mainly from Latin, Italian and Ottoman Turkish. During all periods of the Greek language, loan words into Greek acquired Greek inflections, leaving thus only a foreign root word.Another distinctive characteristic of the Greek language is its powerful compound-constructing ability. The speaker is able to combine basic or derived terms in order to construct compounds that express in one word what other languages would express in an entire sentence. This linguistic mobility is entirely absent from Latin and its offspring languages. In the Homeric language, Thetis - the mother of Achilles, is described as "δυσαριστοτόκεια", meaning "she who to her bad fortune gave birth to the best", in pure Modern Greek - "πικρολεβεντομάνα". Greek's constructing capability is being frequently borrowed by modern languages such as French and English in order to produce monolectic compounds, often by using directly Greek words (e.g. biology < bios + logos; microscope < mikros + skopeein) or by applying imported Greek rules on foreign words. For that reason Greek has always been one of the traditional languages of western science, mainly the natural sciences i.e. physics, chemistry, biology, geography, medicine etc.