So I recently had an advertisement project in my German class and our teacher helped us with the scripts. One line that I originally wrote was "Vorher, ich konnte keinen stall bauen. Jetzt, ich kann!" My teacher then corrected it to "Vorher, konnte ich keinen stall bauen. Jetzt, kann ich!" (He noted that I had incorrect word order). I've been contemplating this word order for a while now, but I just don't understand why my original word order was incorrect. Can anyone help me understand?
In statements such as these examples the conjugated verb is always the second element in the sentence. Both of these sentences start with an adverb, so the subject must move to after the verb allowing the verb to remain second.
Your teacher isnt the best, at least his german isnt. "Vorher konnte ich keinen Stall bauen. Jetzt kann ich!". These commas are wrong and I'd say they are confusing. In a main clause you must place the verb on the second position. Vorher and Jetzt take position one, followed by the verb. (You could also place the time statement at a different position and start with Ich on position one but still followed by the verb on position two). Stall is a noun.
The german word order is pretty free, so you can swap many things, but a verb is needed on position two.