The issue of the balance that teachers should seek between using the target language (TL) and the students’ first language (L1) in the second / foreign language classroom is controversial. For so long, foreign language teaching has been dominated by the principle that teachers should use only the target language (TL) and avoid using the mother tongue (L1) except as a last resort.

The main rational for advocating maximal use of TL also called ‘monolingual principal’ is that for most students, the classroom is the only opportunity they have for exposure to the language. Krashen (1985) claims that languages are learnt most effectively when learners are exposed to lots of comprehensible input within contexts of real communication. 

Otherwise, explaining difficult grammar, terminology ( vocabulary ), and disciplining are considered to be the most common reasons for using L1. These three dimensions of pedagogical communication not just establish constructive relationships but also ensure understanding and maintaining a disciplined environment.

  In my humble opinion, I believe there are a large number of potentially valuable teaching techniques that exploit the L1 as a basis for learning;

·      At the presentation stage :  the L1 can be an efficient  way of clarifying the meanings of words, structures, or utterances, so that students can progress more quickly.

·      At the practice stage : underlying the use of wider interpretation ( for different cultures ) and translation as tools for learning.

·      At the production stage : teachers may design activities in which students start from situations of L1 use and these will serve as an input or stimuli for TL use.

To conclude, L1 can be the most important ally a foreign language can have if it is used systematically ( by the use of proper methods and approaches ) and selectively  ( when, where, how…etc. to use it ).