The use of "Mögen"
A few days ago, I was given a workbook and grammar guide entitled Learn to Speak German (pub. 1999). Looking through it, I have noticed under the entry for mögen that:
- Mögen is common only in the subjunctive mood, möchte.
- In the other moods, mögen is rarer and mainly used when negative (e.g., Ich mag Zitronen nicht) or to indicate possibility (i.e., may or might).
- To like to perform an action is shown with the adverb gern(e); to like something is shown with the verb gefallen.
In addition, another one of my grammar books (1961) uses the constructions haben ... gern to indicate likes an object, although I have found that, not surprisingly, this idiom is falling out of use.
Despite this, Duolingo still gives us statements like Ich mag Zucker. I am curious; is this a result of an oversimplified/generalised translation of mögen as to like, or has German speech further evolved from 1999 to now so that mögen is now used commonly like the English to like?
"Ich mag xy" is a completely normal sentence and was in use as long as I can remember (which was before 1999...). It's because you can use "gefallen" for something that appeals to your visual and auditive tastes, but not for something you like to eat. If you say "mir gefallen Äpfel", then you like their shape. If you say "ich mag Äpfel", then you probably like their taste or whatever uses you might have for them.
I think you may be overcomplicating things a bit there... "Mögen" is used all the time, just like the word "like", it's an essential item of vocab and one of the first words you'll use in basic conversation when expressing likes and dislikes.
"Gefallen" can be used for things like clothing, music, art, people, but never food (unless you're talking about the visual aesthetics of it).
"Gernhaben" is mostly used to express affection towards people, although not exclusively, it also applies to situations. E.g. "Er hat es nicht gern, wenn man ihn stört" (He doesn't like to be bothered/disturbed, literally: He doesn't like it when one bothers/disturbs him).
But "mögen" works for everything, so stick with that in the beginning.
The basic verb form is mögen while the subjunctive form is möchte:
- etwas mögen = to like something
- jemanden mögen = to like someone
- ich möchte (gern) etwas tun = I would like to do something
- ich möchte (gern) etwas haben = I would like to have something
Please have a look at the conjugation table: