Learn Polish: Impreza była świetna, ale byłem tam sam. - The party was great, but I was there alone.

In Polish, past tense verbs change depending on the gender of the subject. In the first half, była (was) is the 3rd person singular feminine form, which matches the feminine noun impreza (party). In the second half, byłem means "I was" and is the 1st person singular masculine form.

If a woman is speaking, how does the second half of the sentence change?

A female speaker must use the feminine form for "I was", which is byłam instead of byłem. She also needs to change the adjective for "alone" to match her feminine gender: sama instead of sam. The second half becomes: ...ale byłam tam sama.

I learned that we use the Instrumental case after the verb "to be". Why is świetna in the basic Nominative case?

You only use the Instrumental case when you use a noun (or an adjective + noun) to describe the subject, like in the sentence "To była świetna impreza" (It was a great party). However, when you use only an adjective to describe the subject, like świetna (great) in this sentence, it stays in the basic Nominative case.

Where is the Polish word for "I" (ja) in the second part of the sentence?