Verbs used with either dative object or prepositional object

Question

Sometimes when I look up words in a dictionary, there are verbs where the dictionary gives me the option to use them either with a dative or a prepositional complement, e.g.:

sich einer/an eine Gruppe anschließen

einen Text der/an die Tafel anschreiben.

Both complements can be used grammatically; however, I wonder 1. whether there are semantic differences between these structures?, 2. If there are no semantic differences, then which structure is more frequent in everyday speech?

My question isn't about those specific examples but more to get a general observation as there might be hundreds of other similar verbs.

Answer 1

This is hard to answer generally, any answer might be on the verge of oversimplification.

Very generally, you can assume that Language, specifically everyday Language, is going to find the easy way out, the easiest way to express a matter. If it doesn't, it might be going to end up sophisticated, of elevated style, or even highbrow (you might, in cases, aim for the first and second, but maybe not for the third).

The easiest way out for the native speaker is using a preposition: In most cases the preposition will clearly rule a specific case, and can be used without much thinking. You can also expect to be understood better, because the preposition adds further redundancy to your sentence other than the case only. Most people will thus, in everyday speech, generally go for the preposition - It is just simpler to use.

Written language like newspaper articles and books have other preferences, though. Style, brevity and being to the point might be more important. In a newspaper article, you might preferably use sich einer Gruppe anschliessen rather than sich an eine Gruppe anschliessen. But still, there's a limit - Your second example will very probably not be used by anyone without a preposition - be it spoken language or in writing, no one will ever say or write ich habe den Text der Tafel angeschrieben.

Also note there might be standing idioms that either prefer the one or the other (sich einer Gruppe anschließen might be considered such an idiom).

For a language learner and if unsure, the rule is maybe clear: Go for the prepositional object construct, it is simpler to learn and use - It's just easier to get it wrong without. Once you manage to use the finer points of the language, you will start to develop a feel when you can use dative objects.

Answer 2

Example 1, "sich einer/an eine Gruppe anschließen" = correct: Concerning a group, it is correct to say e.g. "Sie möchte sich einer Gruppe anschließen" and it is also correct to say e.g. "Sie wollte sich aber nicht an eine Gruppe anschließen". But in another context, you would say e.g. "Ich kann mich Ihrer Meinung nicht anschließen" rather than "Ich kann mich nicht an Ihre Meinung anschließen" (which wouldn't be incorrect, but a bit awkward).
Example 2, "einen Text der/an die Tafel anschreiben" = not correct: You may say e.g. "Er soll den Text an die Tafel schreiben" or, depending on the smaller size of the “Tafel”*), "Er soll den Text auf die Tafel schreiben", - in both cases without the prefix “an-“! The verb "anschreiben" is used with quite different meanings, e.g. "jemanden anschreiben" analogue to "jemanden ansprechen"; or e.g. instead of paying your bill you tell the innkeeper (who knows you well enough), er soll “anschreiben”, meaning that you’ll pay him later. *) Up to the Sixties, there wasn’t only the big blackboard (Tafel) in German classrooms, but each pupil had a small blackboard (Schiefertafel) of his own.