Learn Hardcore Dutch: In de keuken staan manden; er liggen er drie in de kast. - There are baskets in the kitchen; there are three of them in the cupboard.

You can test the partitive er by replacing it with ervan/daarvan: Drie daarvan liggen in de kast (“three of them are in the cupboard”). The first er cannot be replaced that way; it’s just the dummy subject.

Can I drop one of those er’s?

Dropping the first (dummy) er in a neutral statement is usually wrong or very odd: you want Er liggen … or, if you front something else, keep it after the verb: In de kast liggen er drie.
Dropping the partitive er gives Er liggen drie in de kast. That’s common in speech when the category is obvious from context, but in careful writing “Er liggen er drie” or “Er liggen drie manden” is clearer.

Why is it In de keuken staan manden (verb before the subject) and not Manden staan in de keuken?

Dutch main clauses obey the verb-second rule. If you put a non-subject element first (here, the place phrase In de keuken), the finite verb must come second, and the subject follows it: [In de keuken] [staan] [manden]. If you start with the subject instead, you get Manden staan in de keuken—also correct, but with different emphasis.

Could I also say Er staan manden in de keuken or In de keuken staan er manden?

Yes to both. Er staan manden in de keuken is the most neutral existential word order. With the location fronted, both In de keuken staan manden and In de keuken staan er manden are possible; adding er sounds a bit more conversational.

Why is there no article before manden?

Indefinite plural count nouns typically take no article in Dutch when you’re just stating existence/availability: (Er) staan manden. If you mean specific baskets, you’d use de manden or a determiner like die manden.

Why are the verbs plural (staan, liggen)?

The logical subjects are plural:

manden (baskets) → staan.
er drie (three of them) → liggen. With a singular subject you’d use singular: Er staat één mand in de keuken; Er ligt er één in de kast.

Why use staan in the kitchen clause but liggen in the cupboard clause?

Dutch often prefers specific “posture” verbs for location:

staan: objects upright on a base (bottles, vases, upright baskets).
liggen: objects horizontally or lying flat (books, papers, toppled baskets).
zitten: items contained/embedded/fixed in something (e.g., Er zitten eieren in de doos).
hangen: suspended.

So the sentence suggests upright baskets in the kitchen and three lying flat in the cupboard. Depending on how you picture it, In de kast staan er drie could also be fine.

Could I just use zijn instead of posture verbs? For example, Er zijn manden in de keuken.

It’s grammatical, but less idiomatic in everyday descriptions of where things are. Dutch usually picks staan/liggen/zitten/hangen. Use zijn if you really want to stress existence rather than posture.

If I front the location of the second clause, where does er go?

After the verb: In de kast liggen er drie. The finite verb still goes second (after the fronted phrase), and the dummy er follows the verb. Don’t say In de kast er liggen drie.

Could I avoid the partitive er by repeating the noun?

Yes: Er liggen drie manden in de kast. That’s fully natural and avoids the double er.

Can I use zitten here instead of liggen?

Only if you conceptualize them as “sitting/being contained” in the cupboard rather than lying or standing: Er zitten er drie in de kast. For many objects inside containers, Dutch uses zitten by default (e.g., Er zitten snoepjes in het potje), but for larger standalone objects like baskets, staan/liggen is more common.

What about replacing in de kast with daarin/erin?

If the cupboard has already been mentioned, you can pronominalize:

Daarin liggen er drie (neutral, a bit emphatic on “in there”).
Er liggen er drie daarin/erin is also possible; speakers often put (daar)in toward the end. Note you may end up with multiple er’s; that’s allowed but can sound heavy, so many writers prefer daarin.

Is the semicolon necessary?

No. It just links two closely related independent clauses. You could use a period: In de keuken staan manden. Er liggen er drie in de kast. Or a coordinator: …, en er liggen er drie in de kast.

Why is it de keuken / de kast / de mand, not het?

These nouns are common gender (de) nouns. There isn’t a foolproof rule to predict de/het; you learn each noun’s gender with its article. Plurals are always de: de manden.

Could I say op de kast instead of in de kast?

Only if they’re on top of the cupboard. In de kast = inside it; op de kast = on its top surface. Dutch is quite literal with these prepositions.