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"Naive" is an adjective which is often translated as "ingenuo", and "gullible" is an adjective which is often translated as "crédulo". Learn more about the difference between "naive" and "gullible" below.
naive(
nay
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iv
)An adjective is a word that describes a noun (e.g., the big dog).
a. ingenuo 
Don't be so naive, Rory. Luke is clearly taking advantage of you.No seas tan ingenua, Rory. Luke claramente se está aprovechando de ti.
You're more naive than I thought if you think he'll keep his word.Eres más ingenuo de lo que pensaba si crees que va a cumplir con su palabra.
b. inocente 
You can't fool me. I'm not some naive child.No me puedes engañar. No soy un niño inocente.
c. simplista 
The article put forward a very naive perspective of the progress made in equal rights.El artículo presentaba una perspectiva muy simplista del progreso que se ha hecho en la igualdad de derechos.
d. cándido 
Don't be so naive! It's common knowledge that the mayor is corrupt.¡No seas tan cándido! Es conocimiento común que el alcalde es un corrupto.
2. (fine arts)
a. naif 
There is a large naive mural on the wall of the community center.Hay un mural naif grande en la pared del centro comunitario.
gullible(
guh
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lih
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buhl
)An adjective is a word that describes a noun (e.g., the big dog).