The First Conditional

The first conditional is used to refer to the “present or future” where “the situation is real”. The first conditional refers to a possible condition and its probable result. In these sentences the if clause is in the simple present, and the main clause is in the simple future.

IF CLAUSE	MAIN CLAUSE
If + simple present	simple future
If this thing happens	that thing will happen.
If you don't hurry	you will miss the train.
If it rains today	you will get wet.

First Conditional (Structure)

More examples:

• If it rains today, I'll stay at home.
  Si llueve hoy, me quedaré en casa.
• If he is busy now, I will come back tomorrow.
  Si está ocupado ahora, regresaré mañana.
• If I have time, I'll visit my parents this afternoon.
  Si tengo tiempo, visitaré a mis padres esta tarde.
• If it is warm tomorrow, we'll go to the beach.
  Si está caluroso mañana, iremos a la playa.
• If it is cold, you must wear warm clothes.
  Si está frío, debes usar ropa abrigada.
• If he doesn't do his homework, he can not go to the party.
  Si él no hace su tarea, no puede ir a la fiesta.
• If she doesn't call you, you can call her.
  Si ella no te llama, tú puedes llamarla.
• If you work hard, you may become a millonaire someday.
  Si trabajas duro, puede que te conviertas en un millonario algún día.

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Reinforces what was learned:

http://www.aprenderinglesrapidoyfacil.com/2014/04/23/ejercicios-condicional-uno-first-conditional-exercises/