Perro vs. can
In Spanish, both perro and can translate to dog, but they are used in vastly different contexts. The main difference lies in their level of formality and commonality, with perro being the everyday standard and can being a more formal, technical, or literary term.
Perro
A1This is the universal, common, and everyday word for dog. You will hear and use perro in almost all casual and general situations, regardless of the dog's breed, size, or age. It has a feminine form, perra, for a female dog.
Mi perro le encanta jugar en el parque.
(My dog loves to play in the park.)
La perra de mi tía tuvo seis cachorros.
(My aunt's dog had six puppies.)
Ten cuidado, ese perro parece perdido.
(Be careful, that dog looks lost.)
¿Cómo se llama tu perro nuevo?
(What is your new dog's name?)
Adoptamos un perro de un refugio de animales.
(We adopted a dog from an animal shelter.)
Hace un día de perros, no para de llover.
(The weather is awful, it won't stop raining.)
Can
B2This is a formal, technical, or literary term for dog. It is rarely used in spoken, everyday conversation. You will typically find can in scientific writing, official contexts like police or military units, dog show terminology, and in literature for a more poetic or elevated tone. Its plural form is canes.
El concurso premió al mejor can de la exposición.
(The contest awarded a prize to the best dog of the show.)
La unidad canina de la policía inspeccionó el edificio.
(The police's canine unit inspected the building.)
El lobo es el ancestro salvaje del can doméstico.
(The wolf is the wild ancestor of the domestic dog.)
El poema describía al fiel can esperando a su amo.
(The poem described the loyal dog waiting for its master.)
El estudio analiza el comportamiento de diferentes canes.
(The study analyzes the behavior of different dogs.)
La agilidad de este can es impresionante.
(The agility of this dog is impressive.)
Summary
In short, always use perro when talking about a dog in your daily life. It is the correct and natural choice for conversation. Reserve can for formal or specialized contexts; you will primarily encounter it in writing, such as in scientific articles, official reports, or literature. Think of it as the difference between dog (perro) and the more formal canine (can).