A Thai sentence is made up of a number of invariable words, without case, gender, number, tense or mood. The usual order is subject-verb-object. Adjectives always follow the noun they quality.

Gender and number are expressed with the help of auxiliaries, as in most of the languages of South-East Asia. Temporal relations are also expressed by auxiliaries, often verbs, which according to their place in the sentence may refer, for example, to the past or to a future eventuality. Thus ma = "come", ca-ma = (I, you, he, etc.) "will come", dai-ma = (I, you, he, etc.) "has come". In place of prepositions, conjunctions or articles Thai uses terms of relationship, which are not always necessarily expressed. Thus pho luk (pho "father'', luk = "child") can mean "father and child", "father or child" or "father of the child". If the context is not sufficiently clear it may be necessary to insert between the two noons a term expressing relationship, like lae ("and"), ru ("or") or khong, a term meaning "belonging to", "of".

Besides the Bangkok dialect which has become the national language there are many other Thai dialects, the most important of which are the Khorat dialect and the dialect of northern Thailand. The structure of the language remains the same, and the differences of vocabulary are not great.

The differences between social classes are clearly marked. Thus the word kin is the lower class term for "eat". People of a higher social class will prefer to say rapprathan or than, a word which is also used by subordinates addressing their superiors. The use of personal pronouns is a very subtle art in which the person speaking must establish his relationship to the person he is addressing in terms of age, social class and rank, for the choice of pronoun depends on the person who is speaking, the person who is being spoken to and the person who is being spoken about. Contact with western languages, however, has produced a trend towards the simplification of everyday language.

The written language (apart from the language of the newspapers, which has its own particular expressions and formula) uses more elaborate forms which may he difficult for a westerner knowing only the spoken language to understand.

More elaborate still is the vocabulary used in addressing Buddhist monks or members of the royal family. In speaking to the King or a high dignitary or in speaking about them, even in the press, it is necessary to know the royal vocabulary or ratchasap. The court language is taught in schools but used only in the royal household. Some Thais are only imperfectly acquainted with it, and may prefer to speak in English rather than in imperfect Thai, which would be regarded as bad form.