A, an, the, or nothing

Articles are a, an, and the. Sometimes you use nothing.

Four choices

A / an = one, not special yet. The = we both know which one. Nothing = in general. Not every noun needs the.

One, known, or all

I bought a brush. The brush is blue. Brushes are useful — no article, the idea in general.

Every noun needs the. — no
A, the, or nothing — three real jobs. — yes