As a proficient speaker, it isn't that you don't know that the past tense of swim is swam, you've just mistakenly applied the regular rule to an irregular verb. You're unlikely to make this kind of error morę than a smali portion of the time, and may never say "swimmed" again. Your competence is fine - you know how to conjugate irregular English verbs, it is your performance that has let you down.
Though linguists have sińce realized that competence is not the only thing worth studying in Linguistics (thanks to contributions of linguists like William Labov, who popularized sociolinguistics), but the distinction remains useful, primarily because it allows those studying language to differentiate between a speech error and not knowing something about a language. Linguists use this distinction to illustrate the intuitive difference between accidentally saying swimmed and the fact that a child or non-proficient speaker of English may not know that the past tense of swim is swam and say swimmed consistently.
11. vocabuiary, listening, reading, writing, grammar, speaking,
12. a) Reading:
v Multiple choice questions
v Matching writen descriptions with pictures of the items v Transfering writen information to charts, graphs v Choosing the best summary of a paragraph or a whole text v Matching jumbled headings with paragraphs
v Inserting sentences provided by the examiner in the correct place in the text
b) Listening:
v Completing charts with facts and figures from a listening text v Identifying which of a number of object is being described v Identifying which says what
v Identifying whether speakers are enthusistic, amused v Following directions on a map and identifying the correct place
c) Writing:
v Writing compositions and stories v' Transactional letters'
v Information leaflets about their school or a place in their town v Set of instructions for some common task v Newspaper articles about a recent event
d) Speaking:
v An interviewer questioning candidate about themselves v' information gap' v' Decision making'
v Using picture for candidates to compare and contrast v Role-play activities