Use 'a'

We use a if a single common noun is NOT:

· Mentioned previously
· Specific
· A representative noun
· Preceded by another determiner
· Preceded by a possessive
· Uncountable
· Preceded by a clause marker
· A noun that follows a preposition that prohibits an article
· In a series after THE
· A gerundial
· The name of an uncommon ailment

A noun preceded by a is almost always non-specific. The use of a indicates that the speaker (or writer) is referring to one person, place or thing among many,

e.g.

A young lady lives next door.

Would you like a doughnut?

Toshimi is a member of the soccer club.

???Toshimi is the member of the soccer club???

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