In most conjugations, -IR and -ER verbs have the same endings!
Regular -ER verbs follow this conjugation:
Yo
Tú
Él / Ella / Usted
o
es
e
Nosotros
Vosotros
Ellos / Ellas / Ustedes
emos
éis
en
Regular -IR verbs follow this conjugation:
Yo
Tú
Él / Ella / Usted
o
es
e
Nosotros
Vosotros
Ellos / Ellas / Ustedes
imos
ís
en
Many -er and -ir verbs are BOOT VERBS! This means that they undergo a change when conjugated in the forms:
Yo
Tú
Él / Ella / Usted
Ellos / Ellas / Ustedes
Here are some of the most common boot changes! (Verbs with boot changes are bolded)
O -> UE
U -> UE
E -> I
E -> IE
Ejemplos:
Volver - To return / To go back
Querer - To want
Poner - To put
Creer - To believe
Conocer - To know (people/places)
Ver - To see
Saber - To know (information)
Tener - To have
Hacer - To do / To make
Poder - To be able to
Parecer - To seem / To appear
Perder - To lose
Entender - To understand
Leer - To read
Traer - To bring
Nacer - To be born
Comer - To eat
Pedir - To ask for
Decir - To say / To tell
Seguir - To follow / To continue
Venir - To come
Salir - To leave
Vivir - To live
Sentir - To feel
Escribir - To write
Producir - To produce
Ocurrir - To occur
Recibir - To receive
Permitir - To permit
Servir - To serve
Abrir - To open
Dormir - To sleep
Repetir - To repeat
Decidir - To decide
Descubrir - To discover
Morir - To die
Remove the ‘er/ir’ and replace with the proper ending (according to the subject) and check to see if there are any boot changes! (Some -AR verbs have boot changes too, though it’s less common).
Ejemplos:
Yo + entender = Yo entiendo
Tú + poder = Tú puedes