La respuesta rápida

Usa un adjetivo posesivo — my, your, his, her, its, our, their — justo antes de un sustantivo para mostrar de quién es algo. Se dice my book, no I book.

La regla

Un adjetivo posesivo siempre va antes de un sustantivo y nunca cambia si el sustantivo es singular o plural. La palabra que eliges depende del dueño, no de lo que se posee: his car y his cars usan las dos his, porque el dueño (un hombre) no cambia.

No confundas un adjetivo posesivo con un pronombre sujeto. I es el sujeto de la frase (I live in Rome); my muestra posesión (My house is in Rome). Las dos palabras nunca se sustituyen entre sí.

Forma

Ejemplos

• This is my phone.
• Is that your jacket?
• Tom is happy with his new bike.
• Anna loves her garden.
• The cat is cleaning its paws.
• We keep our books on this shelf.

Errores frecuentes

• ❌ I book is on the table. → ✅ My book is on the table. El adjetivo posesivo va antes del sustantivo, nunca el pronombre sujeto.
• ❌ She lost his phone. (sobre una chica) → ✅ She lost her phone. His y her siguen el género del dueño, no del objeto poseído.
• ❌ The dog wags it's tail. → ✅ The dog wags its tail. Its sin apóstrofo muestra posesión; it's significa it is.
• ❌ Their over there with there friends. → ✅ They're over there with their friends. Their muestra posesión, there es un lugar.