Linguistic competence and performance
One a clearly defined object of investigation, the other less clear
We can agree about what things mean or don’t mean or or how they should be said better or that they mean more than one thing, and if they do mean more than one thing, how many things they mean. But as well as saying what we mean to say, we often don’t finish our sentences, or even say the exact opposite of what we mean to say, perhaps missing out the word not.
Competent language (now often referred to as ‘i-Language’ or ‘internal language’) is what we mean to say. Performance (or ‘e-Language’ or ‘external language’) is what we actually say.
The child learning a language is in the position of a player at the logical game of Mastermind or Super Mastermind where the scoring is erratic. The child is getting false evidence about his or her learnability target from each and every unfinished or incorrect sentence. The child learner’s problem is compounded by the fact that there is no way of knowing how much of what is known as the ‘primary linguistic evidence’ is defective or how bad the defects are. Somehow children manage to disregard the misleading evidence of actual performance in favour correctly defined competence. Exactly how children mangage this feat we can, right now, only deduce from indirect evidence.