1. Lesson 1 Usage
Ordinal Numbers

2. First, Second, Third, etc. are called ordinal numbers (for putting things in order). The regular counting numbers are called cardinal numbers.
Primero(a)
Segundo(a)
Tercero(a)
Cuarto(a)
Quinto(a)
Sexto(a)
Séptimo(a)
Octavo(a)
Noveno(a)
Décimo(a)
First
Second
Third
Fourth
Fifth
Sixth
Seventh
Eighth
Ninth
Tenth

3. Ordinal numbers precede the nouns they modify.
El cuarto niño es mi hijo.
The fourth child is my son.
He terminado en séptimo lugar.
I have finished in seventh place.
Primero and Tercero shorten to Primer and Tercer when describing something singular and masculine.
Soy el primer hijo de mi familia.
I am the first son in my family.
Martes es el tercer día de la semana.
Tuesday is the third day of the week.