Learn German: Ein praktischer Herd ist teuer. - A practical stove is expensive.

In this sentence, the stove (Herd) is the subject, which means it is in the nominative case. Since Herd is a masculine noun (der Herd), and the word ein doesn't have an ending to show this, the adjective has to do the heavy lifting. It takes the masculine strong ending -er.

Why doesn't the adjective teuer get an ending too?

In German, adjectives only get endings when they are placed directly in front of a noun (like praktischer is before Herd). When an adjective comes after a verb like ist to describe the subject, it is called a predicative adjective and stays in its basic, unchanged dictionary form.

Since ein is used for both masculine and neuter nouns, is there a clue here that tells us the gender of Herd?

Yes! Because the article ein doesn't show the gender in the nominative case, looking at the adjective ending is a great trick. The -er on praktischer tells us that the noun must be masculine. If Herd were a neuter noun, the sentence would start with Ein praktisches.

If we moved teuer in front of the noun to say 'an expensive stove', how would it be spelled?