Sadhu Bhasa or chaste language, is an old written form of the bangla language, later supplanted by another form called chalita bhasa, or colloquial language, which is now in common currency. While Sadhu Bhasa is literary, Chalita Bhasa is the language of daily use. This phenomenon of two standards, a high and a low, is known as diglossia in linguistics.

The syntax of Bhasa is more defined; the use of tatsama (literally, the same as that, meaning Sanskrit) words is more frequent. The forms of pronouns, verbal endings and others are longer than they are in the spoken form. While Chalita Bhasa conforms to phonological changes, Sadhu Bhasa has changed very little over time. This phenomenon is reflected in the use of vowel harmony and vowel mutation in the colloquial form. The colloquial form is somewhat fast-paced while the chaste form is grave.

Sadhu Bhasa bifurcated into two forms in the nineteenth century: Vidyasagari, or the form used by iswar chandra vidyasagar, and Bankimi, or the form used by bankimchandra chattopadhyay. Vidyasagari was also used by akshay kumar datta. sanskrit words were abundant in Vidyasagari, which made an explicit effort to avoid non-Sanskrit words. Bankimi was used by haraprasad shastri, dinesh chandra sen, rabindranath tagore as well as by mir mosharraf hossain and ismail hossain siraji. Although this form also made heavy use of Sanskrit words, non-Sanskrit words were also used.

Two examples from Vidyasagar and Bankim's Sadhu Bhasa are the following: 'এই পরম রমণীয় એઐােন িকয়ਅਉণ সਗরণ কিরয়া৴ রাজকুমার অশੴ হইেত অবতীণગ হইেলন৴ এবং সমীপবতગী বকুলবৃেਉর એকেਬ অশੴবਬন ও সেরাবের অবগাহনপূবગক৴ એੱান কিরেলন৵ অনੰ੪র৴ অনিতদূরবতગী োবািধেদব মহােদেবর মি੯দের পઝেবশপূবગক দশગন৴ পূজা৴ ও পઝণাম কিরয়া িকয়ਅਉণ পের বিহগગত হইেলন৷' (Vidyasagar, vetalpanchavingshati) and 'অেনক িদন অানে੯দািਢত সਔীত ੂিন নাই৴- অেনক িদন অান੯দ অনুভব কির নাই৷ োযৗবেন যখন পৃিথবী সু੯দর িছল৴ যখন পઝিত পুেઊপ পুেઊপ সুগਬ পাইতাম৴ পઝিত পਠমমગের মধুর শਲ਼ ੂিনতাম৴ পઝিত নਉেਠ িচਠা-েরািহনীর োশাভা োদিখতাম৴ পઝিত মনুষઘ-মুেখ সরলতা োদিখতাম৴ তখন অান੯দ িছল৷ পৃিথবী এখেনা তাই অােছ৴ িকੰ੫ এ হખদয় অার তাই নাই৷' (Bankimchandra, Krishnakanter Will).

The Bankimi Sadhu form was more or less used in the contemporary literature. During this period, the standard written form of Bangla was Sadhu Bhasa, being used in correspondence, prose and other such works across Bengal; this was most used in official documents and legal papers. These days, the form is almost absent from daily life and literature. [Mohammad Daniul Huq]