In English, when you want someone else to do something, you use an object and an infinitive verb: "I want you to keep the wetsuit."
In Swedish, when the subject changes—meaning the person who "wants" is different from the person who performs the action—you must use an att-clause (a "that"-clause) followed by a conjugated verb.
Swedish literally says "I want that you keep...":
| I want you to keep the wetsuit after the diving course. | Jag vill att du behåller våtdräkten efter dykkursen. |
| I want you to empty the air tank. | Jag vill att du tömmer lufttuben. |
"Skulle vilja" and Other Subjects
This mandatory att-clause rule applies to any expression of wanting, including the polite skulle vilja (would like). "I would like you to..." becomes Jag skulle vilja att du...:
| The instructor would like us to take the diving course together. | Instruktören skulle vilja att vi tar dykkursen tillsammans. |
It also applies in the third person, when talking about what someone else wants another person to do:
| The instructor wants the diver to keep his air tank. | Instruktören vill att dykaren behåller sin lufttub. |
Negation and Complex Instructions
If you want someone not to do something, you negate the main clause with inte (vill inte att):
| I do not want the flippers to touch the bottom. | Jag vill inte att simfenorna rör bottnen. |
You can combine these att-clauses with other linking words, like istället för att (instead of) or innan (before):
| She wants us to float instead of sinking to the bottom. | Hon vill att vi flyter istället för att sjunka till bottnen. |
| He wants you to empty the mask before you get the certificate. | Han vill att du tömmer masken innan du får certifikatet. |