Learn Polish: Zaimek to małe słowo, więc przyimek to też małe słowo. - A pronoun is a small word, so a preposition is also a small word.

This sentence equates two things: a pronoun (Noun) and a small word (Noun). In Polish, when you say a Noun is a Noun, you can use the particle to instead of the verb być (to be). When you use to, both nouns stay in the Nominative case, which is their basic dictionary form.

If I wanted to use the verb jest instead of to, how would the sentence change?

If you use the verb jest (is), the noun phrase that follows it must take the Instrumental case. The sentence would become: Zaimek jest małym słowem, więc przyimek jest też małym słowem. Using to lets you keep everything in the Nominative case, which is often much simpler!

Are the words zaimek (pronoun) and przyimek (preposition) related to each other?

Yes! They both come from the root word imię (name, or historically, noun). A zaimek is a word used instead of a noun (za means for/instead of), while a przyimek is a word placed next to a noun (przy means by/next to).

Why is też (also) placed right after to in the second half of the sentence?

In Polish, też usually comes right after the word it logically emphasizes or relates to. Here, placing it immediately after the linking word to makes the sentence flow naturally, directly following the 'is' concept.