Some general issues

A speaker of a language knows how to understand a novel text (spoken and maybe written) and to produce a novel text (spoken and maybe written). For example, a speaker of English or Spanish could understand or produce this story or something similar.
To the extent that knowledge of one's language is true of that language and not (all) others, this knowledge can be seen as conventional. Knowledge which is true of all languages (or of all languages of a particular type) is often thought of as universal.
The types of knowledge discussed on the following slides are useful in describing language, but they may or may not be explicitly represented in the minds of language users, and it may be possible to learn a language without making explicit reference to them.
Knowledge of language (competence) is often distinguished from the use that that knowledge is put to (performance). But these may not be clearly distinguished in the minds of language users, and the distinction may not be helpful in computational applications.

Phonetic knowledge

You know how to translate abstract linguistic categories into articulatory gestures.
For example, you know the combination of glottal and tongue movements that are required to execute the syllable /ðə/ (the).
You know how to classify particular acoustic patterns as belonging to particular linguistic categories.
For example, you know how to decide that this waveform represents /ðə/ (the)
You know how to use the patterns of loudness and pitch in your language to help you find boundaries between units.
For example, you know that in English, words tend to be stressed on the first syllable. This helps you decide that in the leaves had fallen off the trees, "fall" is probably the first syllable of a word.
Units: phonetic features

You know what sounds can legally follow what other sounds in your language (phonotactics).
For example, in off the trees, you know that the first consonant is not /h/ because it cannot appear in this position in English.
You know how the same abstract sound gets realized in different ways in different environments.
For example, you know that the two [t] sounds in I will go to Toad's house belong to the same category (phoneme) even though they are pronounced quite differently.
You know how phonological units at one level (for example, phonemes) combine to form phonological units at a higher level (for example, syllables).
For example, you know how the sentence the leaves had fallen off the trees is organized into syllable and higher-level metrical units (with stresses on leaves, fall, and trees).
Units: phonemes, moras, syllables, metrical feet, phonological phrases

You know what order to put, or expect, the morphemes in in a polymorphemic word.
For example, you know to say mess-y and not y-mess.
You know how the sounds in a morpheme change when it combines with another.
For example, you know to pronounce the ed in raked as /t/ and the ed in started as /əd/.
You know how to interpret or produce a word consisting of a novel combination of familiar morphemes.
For example, you can guess what aspartamey means if you know what aspartame means.
Note: morphology is one aspect of language that differs dramatically between languages, with some languages, like Chinese and English, relatively simple, and many others, quite complex. Some Swahili examples: ninaandika 'I write', siandiki 'I don't write', niliandika 'I wrote' sikuandika 'I didn't write', nilikiandika 'I wrote it (book, etc.)', niliiandika 'I wrote it (letter, etc.)', nilichokiandika 'which I wrote (it; book, etc.)', nikikiandika 'if I write it (book, etc.)', hakijaandikwa 'it (book, etc.) hasn't been written', nilimwandikia 'I wrote to him/her', nisingalimwandikisha 'I wouldn't have caused him/her to write',
Units: morphemes

You know what order to put the constituents of a sentence in to signal a particular meaning.
For example, you know to say Frog worked hard and not Frog hard worked.
You know what roles the constituents of a sentence play in the state or event referred to by the sentence.
For example, you know that in he will never know who raked his leaves, he is the KNOWER, who raked his leaves the INFORMATION that is (not) known, and leaves the PATIENT of the raking.
You know how certain words have to agree with others, even when failure to agree would not interfere with communication. For example, you know that you should say these messy leaves have covered rather than this messy leaves has covered.
You know where to expect gaps in particular patterns.
For example, you know that in the pile of leaves that Frog had raked for Toad, you should not expect raked to be followed by a direct object (that is, *the pile of leaves that Frog had raked them for Toad is ungrammatical).
Units: phrases, clauses, sentences

You know how words and sentences relate to objects and relations in the world.
For example, you know what kind of a thing to expect the noun rake and what kind of event to expect the verb rake to refer to.
You know how to figure out the temporal relationships among the events and states referred to in sentences.
For example, in the pile of leaves that Frog had raked for Toad blew everywhere, you know that the raking happened before the blowing.
You know how to "find" the thing that is referred to by a definite noun phrase (such as the guy who always parks in front of my driveway).
For example, you know what is referred to by the light in when they each turned out the light.
Units: semantic features, objects, relations, variables, worlds, mental spaces

You know how figure out what anaphors (such as pronouns in English) refer to. For example, in
The leaves had fallen off the trees. They were lying on the ground.
you know that they refers to the leaves and not the trees.
You know how to get somebody to do something for you using language.
For example, you know to say could you pass me the salt rather than you're going to pass me the salt or I want the salt.
You know how the meanings of words such as go and come change with the context.
You know how to begin, end and take turns in particular kinds of discourses, for example, phone conversations, in appropriate ways. For example, you know that it is inappropriate to simply say "good-bye" and then hang up if you want to end a phone conversation.
Units: utterances, discourses, turns

You know what forms sound more formal than others and how to select the forms that are appropriate to the situation.
For example, you know not to write "LOL" in the cover letter for a job application or to say "highly inappropriate" when disciplining your three-year-old daughter (except for comic effect).
You know when somehow has said something that is politically incorrect.