Learn Icelandic: Við vorum að tala um glæpinn. - We were talking about the crime.

Just like in English, Icelandic uses the past tense of the verb to be (vera) plus the main verb to show an ongoing action. Here, we use vorum (we were) followed by að tala (to talk). The að plus the infinitive verb acts like the -ing ending in English, creating the past continuous tense.

Could I just say Við töluðum um glæpinn instead?

Yes, but it changes the meaning slightly. Við töluðum is the simple past meaning we talked, whereas Við vorum að tala is the past continuous meaning we were talking. The continuous form emphasizes that the action was ongoing at that particular moment in the past.

Does the preposition um force a specific case here?

Yes, the preposition um (when it means about) always takes the accusative case in Icelandic. That is why the noun that follows it, glæpinn, must be in the accusative form.

What is the dictionary form of glæpinn and how did it change to this form?

The dictionary form is glæpur (a crime), which is a masculine noun. To make it accusative because of the preposition um, we drop the -ur ending to get glæp. Finally, we add the masculine accusative definite article -inn (the) to the end of the word, resulting in glæpinn (the crime).