La respuesta rápida

Usa this y these para algo cerca de ti, y that y those para algo lejos. Usa this/that para una sola cosa, y these/those para más de una.

La regla

Dos cosas deciden la palabra: la distancia y la cantidad. Al combinarlas, solo queda una opción correcta.

Las cuatro palabras pueden ir solas como sujeto (This is my book) o delante de un sustantivo (This book is mine). El significado no cambia, solo cambia la estructura de la frase.

Forma

Ejemplos

• This is my phone.
• That car, over there, is new.
• These shoes are comfortable.
• Those mountains are far away.
• Is this your bag?

Errores frecuentes

• ❌ This books are mine. → ✅ These books are mine. Un sustantivo plural necesita these, no this.
• ❌ Those car is nice. → ✅ That car is nice. Un sustantivo singular necesita that, no those.
• ❌ I like this shoes here. → ✅ I like these shoes here. Shoes es plural, necesita these.
• ❌ Is that your book, in your hand? → ✅ Is this your book, in your hand? Algo cerca de ti necesita this, no that.