Second language (L2) grammars are by nature prescriptive as they try to guide the learner towards accurate use of the target language. The rules presented in many L2 grammars are often simplified so as to be more accessible to the learner. In many instances, these rules do not provide full coverage of a language structure. Leech (1994), for example, notes that pedagogic descriptions are often not comprehensive, but contain broad generalizations, ie simplifications or 'rules of thumb'. He also notes that while such simplification facilitates learning/assimilation, it can be misleading. There is a rule in English language teaching, for example, stating that 'already' should be used in statements, and 'yet' in interrogatives and negatives:

'I've already done it.'
'Have you done it yet?'
'I haven't done it yet.'

This rule is only a partial truth, however, as it is possible to use 'yet' in statements:

'His addictive personality was yet to manifest itself.' (from COBUILD Bank of English)

Leech, and some other L2 grammarians, would argue that it is necessary to offer simplified rules to learners in order to maximize learning. L2 grammars often use concocted sentences to illustrate grammar patterns as real-world, authentic language texts are sometimes considered too complex to clearly illustrate specific patterns. Recent corpus-based approaches, where large computer databases of language are analysed for frequency of different patterns, attempt to show that there are ways in which the use of authentic language can help us to construct a grammatical syllabus that reflects real-world language use.

In traditional pedagogic and textbook grammar, grammar topics and materials are usually graded; learners have their attention drawn to general rules (similar to Leech's 'rules of thumb'); and there are usually practice exercises to accompany the rules.

Chalker (1994: 34) believes that pedagogical grammars may be comprehensive, but are more useful if modest in aims, and that prescription should be combined with description.

Corder notably believes that grammar should not be the objective of teaching, and that communicative skills should be emphasized:

[P]edagogical descriptions [...] must [...] help the learner learn whatever it is he learns, but are not necessarily what he learns. Pedagogical descriptions are aids to learning, not the object of learning [...] the teaching of grammar cannot be divorced from the teaching of meaning. (Corder,1973: 335-36)