Learn French: La balle est une sphère, pas un cercle. - The ball is a sphere, not a circle.

In French, the word for "ball" changes depending on its size and use. Une balle is generally a small ball used in sports (like tennis or golf). A larger, inflatable ball (like a soccer ball) is un ballon, while a heavy, solid ball (like for bowling or pétanque) is une boule.

Why does the sentence use pas un cercle instead of pas de cercle?

The rule that changes un, une, or des to de after a negative only applies to the direct objects of negated verbs. Here, pas is just contrasting two nouns directly, not negating a verb, so the article un remains. Furthermore, the verb in this sentence is être, which is an exception to the de rule anyway!

Is it possible to say non pas un cercle in this context?

Yes! Using non pas un cercle is perfectly correct and adds a bit more formal emphasis to the contrast. However, simply dropping the non and using pas before the noun is a very natural and common shortcut in everyday French.

Cercle is masculine but sphère is feminine. Is there a rule for the gender of geometric shapes?