Learn Hardcore Russian: Я взял оставленный на скамейке зонтик.

взять means “to take” and is a perfective verb, which implies the action is completed. взял is its past tense, masculine, singular form, so “I took” with the nuance that the taking is finished.

Why is взял in the past masculine form?

Russian past tense verbs agree in gender and number with the subject. Since the speaker (Я) is assumed male here, the masculine form взял is used. A female speaker would say взяла instead.

What is оставленный, and how is it formed?

оставленный is the past passive participle of оставить (“to leave behind”). It’s formed by adding the participial suffix -нн- to the verb stem plus adjective endings. Here it describes the umbrella as “the one left.”

Why is there no relative pronoun like который?

Russian often replaces relative clauses with participial adjectives for conciseness. Instead of saying зонтик, который оставили на скамейке, the participle оставленный performs the same function in a shorter form.

Why is на скамейке in the prepositional case?

The preposition на meaning “on” (when indicating location) governs the prepositional case. Hence скамейка becomes скамейке to express “on the bench.”

Why is зонтик in the accusative case, and why does it look like the nominative?

зонтик is the direct object of взял, so it’s in the accusative case. Because it’s an inanimate masculine noun ending in a consonant, its accusative form is identical to the nominative form.

How do оставленный and зонтик agree in gender, number, and case?

As a participle functioning like an adjective, оставленный must match зонтик in gender (masculine), number (singular), and case (accusative), resulting in оставленный … зонтик.

Could I rephrase this sentence with a relative clause?

Yes. You could say:
Я взял зонтик, который оставили на скамейке.
This uses the relative pronoun который, but is a bit longer than the participial version.

Why is the word order оставленный на скамейке зонтик instead of зонтик оставленный на скамейке?

In Russian, descriptive modifiers (participles, adjectives) typically precede the noun they modify. Putting оставленный на скамейке before зонтик sounds more natural and emphasizes “the umbrella that was left.”