For most languages that have a major class of nouns (not all do) it is possible to define a basic word order in terms of the finite verb (V) and its arguments, subject (S) and object (O). There are six theoretically possible basic word orders: subject verb object (SVO), subject object verb (SOV), verb subject object (VSO), verb object subject (VOS), object subject verb (OSV) and object verb subject (OVS). The overwhelming majority of the world's languages are either SVO or SOV, with a much smaller but still significant portion using VSO word order. The remaining three arrangements are exceptionally rare, with VOS being slightly more common than OVS and OSV being significantly more rare than two preceding ones.
While the first two of these requirements are relatively easy to respect, the latter two are more difficult. In spoken language, there are hardly ever two full nouns in a clause; the norm is for the clause to have at most one noun, the other arguments being pronouns. In written language, this is somewhat different, but that is of no help when investigating oral languages. Finally, the notion of "pragmatically neutral" is difficult to test. While the English sentence The king, they killed has a heavy emphasis on king, in other languages, that order (OSV) might not carry a significantly higher emphasis than another order.
If all the requirements above are met, it still sometimes turns out that languages do not seem to prefer any particular word order. The last resort is text counts, but even then, some languages must be analyzed as having two (or even more) word orders.
Sometimes patterns are more complex: German, and Dutch have SOV in subordinates, but V2 word order in main clauses, SVO word order being the most common. Using the guidelines above, the unmarked word order is then SVO.
Others, such as Latin and Finnish, have no strict word order; rather, the sentence structure is highly flexible. Nonetheless, there is often a preferred order; in Latin, SOV is the most frequent outside of poetry, and in Finnish SVO is the most frequent, and obligatory when case marking fails to disambiguate argument roles, for example Puun kaatoi mies (tree-acc fell-perf man.NOM) ~ A/the man felled the tree but puut kaatoivat miehet (tree-pl.nom/acc fell-perf-3p.pl man-pl.nom/acc) ~ The trees felled the men. Just as languages may have different word orders in different contexts, so may they have both fixed and free word orders. For example, Russian has a relatively fixed SVO word order in transitive clauses, but a much freer SV / VS order in intransitive clauses.
Observing discourse patterns, it is found that previously given information (topic) tends to precede new information (comment). Furthermore, acting participants (especially humans) are more likely to be talked about (to be topic) than things simply undergoing actions (like oranges being eaten). If acting participants are often topical, and topic tends to be expressed early in the sentence, this entails that acting participants have a tendency to be expressed early in the sentence. This tendency can then grammaticalize to a privileged position in the sentence, the subject.
The mentioned functions of word order can be seen to affect the frequencies of the various word order patterns: An overwhelming majority of languages have an order in which S precedes O and V. Whether V precedes O or O precedes V however, has been shown to be a very telling difference with wide consequences on phrasal word orders.
Knowledge of word order on the other hand can be applied to identify the thematic relations of the NPs in a clause of an unfamiliar language. If we can identify the verb in a clause, and we know that the language is strict accusative SOV, then we know that Grob smock Blug probably means that Grob is the smocker and Blug the entity smocked. However, since very strict word order is rare in practice, such applications of word order studies are rarely effective.
The order of constituents in a phrase can vary as much as the order of constituents in a clause. Normally, the noun phrase and the adpositional phrase are investigated. Within the noun phrase, one investigates whether the following modifiers occur before or after the head noun
Within the adpositional clause, one investigates whether the languages makes use of prepositions (in London), postpositions (London in), or both (normally with different adpositions at both sides).
There are several common correlations between sentence-level word order and phrase-level constituent order. For example, SOV languages generally put modifiers before heads and use postpositions. VSO languages tend to place modifiers after their heads, and use prepositions. For SVO languages, either order is common.
For example, French (SVO) uses prepositions (dans la voiture, à gauche), and places adjectives after (une voiture spacieuse). However, a small class of adjectives generally go before their heads (une grande voiture). On the other hand, in English (also SVO) adjectives almost always go before nouns (a big car), and adverbs can go either way, but initially is more common (greatly improved). (English has a very small number of adjectives that go after their heads, such as "extraordinaire", which kept its position when it was borrowed from French.)
Some languages do not have a fixed word order. In these languages there must be a significant amount of morphological marking to disambiguate the roles of the arguments, however there are also languages in which word order is fixed even though the degree of marking would enable free word order. Typologically there is a trend that highly animate actors are more likely to be topical than low-animate undergoers, this trend would come through even in free-word-order languages giving a statistical bias for SO order (or OS in the case of ergative systems, however ergative systems do not usually extend to the highest levels of animacy, usually giving way to some form of nominative system at the latest in the pronominal system). Also there are cases of flexible rather than strict word order, usually these can be unambiguated using methods given above. Free-word-order languages include Latin, Czech, Hungarian, Polish and Russian.
For example, English is SVO (subject-verb-object), as in "I don't know this", but OSV is also possible: "This I don't know." This process is called topic-fronting (or topicalization) and is common. In English, OSV is a marked word order because it emphasises the object, and is often accompanied by a change in intonation.
An example of OSV being used for emphasis: