Breakdown of Это инструмент, которым он лепит скульптуру.
это
this / it is
он
he / it (for a masculine noun) / it (for a neuter noun)
инструмент
the tool
который
which / who / that (relative pronoun)
Questions & Answers about Это инструмент, которым он лепит скульптуру.
Why is it just которым and not с которым?
In Russian, the Instrumental case without the preposition с is used to show the actual tool or instrument used to do an action. If we used с которым, it would mean he is sculpting something together with the tool as a partner (accompaniment), rather than using the tool itself to do the work.
How do we know to use the masculine form которым instead of которой?
The relative pronoun который must match the gender and number of the noun it refers back to. Since инструмент is a masculine singular noun, we use a masculine singular form. Its case (Instrumental) is determined by its role in the second half of the sentence (the object being used to sculpt).
What is the infinitive of лепит, and when do we use this verb?
The infinitive is лепить (to sculpt, mold, or model). It is a very common verb in Russian used whenever you are shaping something by hand out of soft materials like clay, dough, or snow. For example, making a snowman is лепить снеговика and making dumplings is лепить пельмени.
Why must there be a comma before которым?
In Russian, relative clauses (parts of a sentence starting with who, which, or that) must always be separated from the main sentence by a comma. You will almost always see a comma right before any form of который.