Tenses - English has a relatively large number of tenses with some quite subtle differences in their usage. Most learners of English find this difficult to master.
Functions of auxiliaries - Learners of English tend to find it difficult to manipulate the various ways in which English uses the first auxiliary verb of a tense. These include negation (eg He hasn't been drinking. ), inversion with the subject to form a question (eg Has he been drinking? , short answers (eg Yes, he has. ) and tag questions ( has he? ). A further complication is that the dummy auxiliary verb do / did is added to fulfil these functions in the simple present and simple past, but not for the verb to be .
Modal verbs - English also has a significant number of modal auxiliary verbs which each have a number of uses. This complexity takes considerable work for most learners to master.
Vocabulary
Phrasal verbs - Phrasal verbs in English cause a lot of problems for most learners. This is because many phrasal verbs have several meanings and because of the different syntactic patterns.
Word derivation - Word derivation in English requires a lot of rote learning. For example, an adjective can be negated by using the prefix un- (eg unable ), or in- (eg inappropriate ) or dis- (eg dishonest ).
Size of lexicon - The history of English has resulted in a relatively large vocabulary. This inevitably requires more work for a learner to really master the language.
