Learn French: Si tu possédais moins, ces jouets n'encombreraient pas la chambre. - If you owned less, these toys would not clutter the room.

This is a classic 'si' (if) clause structure for hypothetical situations. When you use si followed by the imperfect tense (possédais), the resulting action must be in the conditional tense (encombreraient). It works much like English: 'If you owned [past], they would not clutter [conditional].'

How would we change this sentence to use the restrictive negation ne... que from our current lesson to say 'these toys would ONLY clutter the room'?

You would drop the word pas and replace it with que. The clause would become ces jouets n'encombreraient que la chambre. Remember that ne... que wraps around the conjugated verb just like standard negation, but it translates to 'only' rather than 'not'.

Why does the sentence use moins instead of moins de?

Here, moins (less) is acting as an adverb directly modifying the verb possédais (owned). You only use moins de when it is followed by a noun, such as if you wanted to say moins de jouets (fewer toys).

How is the conditional verb encombreraient formed here?