Musen ligger ved siden af tastaturet på skrivebordet.

Because musen is the definite form of mus.

• en mus = a mouse
• musen = the mouse

In Danish, the definite article is usually added to the end of the noun instead of being a separate word like English the.

Since the sentence talks about a specific mouse, it uses musen.

This is because Danish nouns belong to different grammatical genders:

• common gender nouns usually take -en in the definite form
• neuter nouns usually take -et in the definite form

So here:

• en mus → musen
• et tastatur → tastaturet
• et skrivebord → skrivebordet

You often need to learn each noun together with en or et.

In Danish, you often use specific position verbs where English might simply use is.

Here, ligger literally means lies / is lying, but it is also commonly used for things that are located somewhere, especially when they are resting horizontally on a surface.

So:

• Musen ligger på skrivebordet sounds natural in Danish.
• English would usually just say The mouse is on the desk.

Danish often prefers:

• ligger for things lying down or resting
• står for things standing upright
• sidder for things sitting or attached in a certain way

Ved siden af is a fixed expression meaning next to or beside.

It is best learned as one unit:

• ved siden af tastaturet = next to the keyboard

Literally, the parts are something like:

• ved = by / at
• siden = the side
• af = of

But in practice, learners should remember ved siden af as a complete phrase meaning next to.

Because Danish usually puts definiteness on the noun itself.

So instead of:

• the keyboard
• the desk

Danish says:

• tastaturet
• skrivebordet

That means the ending already includes the idea of the.

The sentence first gives the mouse’s position relative to the keyboard, and then adds where that whole scene is located.

So the structure is:

• Musen = the subject
• ligger = the verb
• ved siden af tastaturet = next to the keyboard
• på skrivebordet = on the desk

This is very natural in Danish. The final phrase på skrivebordet tells you where the mouse and keyboard are.

In normal understanding, it describes the location of the whole situation: the mouse is next to the keyboard, and this is happening on the desk.

So the natural interpretation is:

• the mouse is on the desk
• the keyboard is on the desk
• the mouse is next to the keyboard

In real usage, Danish often leaves this kind of relationship to context, just like English does.

It can be either in principle, because mus means both mouse the animal and mouse the computer device.

In this sentence, the context makes it clear that it means the computer mouse, because it is next to tastaturet (the keyboard) on skrivebordet (the desk).

Grammatically, Danish sometimes allows er, but in this context ligger is much more natural.

• Musen er ved siden af tastaturet is understandable.
• Musen ligger ved siden af tastaturet sounds more idiomatic and Danish-like.

Using the position verb makes the sentence sound more natural.

The basic word order is:

Subject + verb + location information

So:

• Musen = subject
• ligger = verb
• ved siden af tastaturet på skrivebordet = place/location information

This is the normal Danish pattern for a simple statement.

It would be:

En mus ligger ved siden af et tastatur på et skrivebord.

That means A mouse is lying next to a keyboard on a desk.

Compare:

• en mus → musen
• et tastatur → tastaturet
• et skrivebord → skrivebordet

This is a useful way to see how Danish changes nouns from indefinite to definite.

In normal speech, ved is often pronounced with a very soft d, sometimes almost disappearing.

So it may sound roughly like:

• ve or veð depending on the speaker

This is common in Danish, where d can be much softer than English speakers expect.

Yes. Ligger is the present tense form of ligge.

So:

• at ligge = to lie
• ligger = lies / is lying

In Danish, the present tense is often used in cases where English might say either lies or is lying, depending on style.