In linguistics, it is considered important to distinguish errors from mistakes. A distinction is always made between errors and mistakes where the former is defined as resulting from a learner's lack of proper grammatical knowledge, whilst the latter as a failure to utilize a known system correctly.[3] Brown terms these mistakes as performance errors. Mistakes of this kind are frequently made by both native speakers and second language learners. However, native speakers are generally able to correct themselves quickly. Such mistakes include slips of the tongue and random ungrammatical formations. On the other hand, errors are systematic in that they occur repeatedly and are not recognizable by the learner. They are a part of the learner's interlanguage, and the learner does not generally consider them as errors. They are errors only from the perspective of teachers' and others who are aware that the learner has deviated from a grammatical norm.[4] That is, mistakes can be self-corrected with or without being pointed out to the speaker but errors cannot be self-corrected.