Second Language Pragmatics, the study of how L2 pragmatics develops, focuses on how learners acquire the L2 pragmatic system over time (Bardovi-Harlig 2014).
Interlanguage Pragmatics (ILP) lies at the intersection of the study of second language acquisition (SLA) and pragmatics. Interlanguage Pragmatics, like SLA and Pragmatics, is an interdisciplinary field that has been studied from various theoretical, analytical, and methodological perspectives.
ILP is the study of how learners (adults or children) acquire the ability to produce and understand communicative action in a second language, such as refusing an offer for food, asking a professor to write a letter of recommendation, complaining about an unfair grade on the final exam, or knowing when it is appropriate to remain silent in conversation. Pragmatic knowledge, one aspect of learners’ communicative competence, is comprised of two components necessary to communicate effectively in a second language: the first, pragmalinguistic knowledge, refers to the linguistic resources that are available in a particular language and that are necessary to express a specific communicative effect. This includes knowledge of different forms and their meanings. For example, the form ‘I can’t’ (literal form) can be used in English to express a refusal to an invitation. But when refusing an invitation to a birthday party a speaker can select from a variety of other linguistic forms to convey the refusal, for example: ‘Thanks, but I really can’t’; ‘I’m sorry, but I have plans’; ‘I don’t know, I have to think about it’. The second component, sociopragmatic knowledge, refers to knowledge of social conventions at the perception level, such as an awareness of the differences in social distance or social power among interlocutors. For instance, it includes knowledge of what expressions are appropriate (or are not appropriate) to use in a second language when refusing a professor’s advice to take a class or apologizing to a friend for crashing his/her car over the weekend.
ILP is concerned with how second language learners learn how to do things with words over time in the learner’s own country (foreign language settings) or in natural contexts where the target language being learned is spoken by native speakers of the learners’ target language (second language settings) (For additional information on pragmatic knowledge see Leech  and Kasper and Rose [2002, chapter 1]).