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Linking adjectives and infinitives with 'de'

When you want to say that something is easy to do or hard to understand, English links the adjective and the verb with the word to. In Spanish, this exact phrasing often requires the preposition de. For example, if a book is easy to read, you use fácil de leer.

However, this rule only applies when the noun you are describing is the object of the verb that follows. Because English uses the same structure for both specific descriptions and general statements, English speakers often miss this important structural difference in Spanish.

Word list
difícilA1 difficult un problema difícil de resolver fácilA1 easy un libro fácil de leer interesanteA1 interesting un tema interesante de debatir tristeA1 sad una escena triste de ver aburridomA2 boring un libro aburrido de leer agradableA2 pleasant una voz agradable de escuchar cómodomA2 comfortable una silla cómoda de usar complicadomA2 difficult un sistema complicado de usar divertidomA2 funny un juego divertido de jugar duromA2 difficult una noticia dura de aceptar imposibleA2 impossible un ruido imposible de ignorar peligrosomA2 dangerous un producto peligroso de manejar seguromA2 safe un producto seguro de usar sencillomA2 simple un plato sencillo de preparar simpleA2 simple una regla simple de recordar arriesgadomB1 risky una maniobra arriesgada de realizar complicadomB1 complicated algo complicado de explicar desagradableB1 unpleasant una verdad desagradable de oír dolorosomB1 painful una experiencia dolorosa de recordar incómodomB1 uncomfortable unos zapatos incómodos de llevar riesgosomB1 risky una operación riesgosa de hacer complejomB2 complex un tema complejo de explicar entretenidomB2 entertaining una novela entretenida de leer amenomC1 entertaining un libro ameno de leer
The specific object rule

To know whether you need de, look at what the adjective is describing. If the subject of your sentence is the thing receiving the action of the verb, you must connect the adjective and the infinitive with de.

For instance, if you say that a text is easy to read, the text is the thing being read. Therefore, fácil and leer are joined by de.

Este texto es fácil de leer.
(This text is easy to read.)
El programa es complicado de instalar.
(The program is complicated to install.)

You can also use this structure directly next to a noun, just like in English.

Tienen un problema difícil de resolver.
(They have a problem that is difficult to solve.)
Es un plato sencillo de preparar.
(It is a simple dish to prepare.)
When not to use de

The trickiest part for learners is when the sentence makes a general statement using the word it. If you say it is easy to read this text, the word it does not refer to the text. In this case, Spanish does not use de. The adjective connects directly to the infinitive.

Es fácil leer este texto.
(It is easy to read this text.)
Es imposible ignorar ese ruido.
(It is impossible to ignore that noise.)

Compare that last example to the specific object rule. If the noise is the subject of the sentence, de returns.

Ese ruido es imposible de ignorar.
(That noise is impossible to ignore.)
Describing experiences

This pattern is not limited to words like fácil, difícil, and imposible. You can use it with many adjectives to describe how an action feels or how a specific object behaves when you interact with it. Words like agradable, cómodo, interesante, and doloroso are very common in this structure.

El cantante tiene una voz muy agradable de escuchar.
(The singer has a very pleasant voice to listen to.)
Esta silla es bastante cómoda de usar.
(This chair is quite comfortable to use.)
Fue una experiencia dolorosa de recordar.
(It was a painful experience to remember.)
Este libro es muy interesante de analizar.
(This book is very interesting to analyze.)
Summary

When an adjective describes a specific noun that receives the action of a following infinitive, link the adjective and the verb with de. If you are making a general statement starting with the word it, leave de out and put the infinitive right next to the adjective.