| The difficulty of mastering the tenses is something that I think a lot of English speakers overlook. There's a lot of really precise and difficult-to-explain subtleties in English. (Of course, English isn't unique in this regard -- but I feel like certain things are taken for granted). Something that catches a lot of English as second language people out is the correct time to use the gerund form (i.e., the '-ing' form). For instance, (1) I am walking to the shops. is clear -- it is occurring in that moment. But what about the subtle difference between (2a) and (2b)? (2a) I live in Berlin. (2b) I'm living in Berlin. To me -- a native English speaker -- (2b) implies that the speaker generally lives elsewhere, while (2a) doesn't. But they're both technically correct if the speaker is, at that moment, a resident of Berlin. There are more examples I could give. Teaching these sorts of subtleties, though, and mastering them can be very difficult. A final example that I really like, and one that my syntax lecturer used to use a lot: (3) She would have had to have been being watched. Seven (or maybe six, depending on how you view 'watched') verbs in a row! Native English speakers grasp this really intuitively, but non-native speakers may have trouble parsing these into a coherent picture. To illustrate this -- try and gloss this sentence another way while conveying the meaning. If you speak another language, try and translate it! English verbs are hard. |
Regarding your example with the gerund, yes it is subtle, but similar subtleties exist in German, e.g. The difference between perfect and simple past (also exist in English), which many native speakers in both English and German get wrong as well.
An interesting anecdote (which might be related) is, that in my experience having gone to high-school in the US for a year and having done language courses with Australian teachers, that there seems to be much less education on the grammar of the language than in Germany. I often knew the "theory" of English grammar much better than the native speakers (doesn't mean I was better at applying it though).
All that said, mastering English is still difficult, just not due to the grammar. Spelling is one thing, but also the vocabulary is huge. Supposedly Shakespeares vocabulary was 60000 words, the equivalent German poet Goethes was less than 40000.