First Conditional: When vs If

This grammar connects two events in a logical chain. One event depends entirely on the other. We call these two parts the "condition" and the "result." If the condition happens, the result follows automatically. It is like a digital switch. On or off. Yes or no. The most important part to remember is the timing. We are looking forward into the future. Even though we use present tense words in one part, we are talking about tomorrow. It feels a bit like time travel for your verbs. Think of it like a grammar traffic light. The condition is the green light that lets the result move forward.

1. 1Building this sentence is like following a simple recipe. You need two main parts to make it work.
2. 2The Condition: Start with if or when. Use the Present Simple tense here.
3. 3The Comma: If you start with the condition, add a comma after it.
4. 4The Result: Use will or won't plus the base form of the verb.
5. 5Example: If + it rains (Present Simple) + , + I will stay (Will + Verb) + home.
6. 6You can also flip the sentence around. I will stay home if it rains. In this case, no comma is needed. It is like a reversible jacket. Both sides work perfectly, but the style changes slightly.

Use if when you are not sure about the outcome. It is for a possibility. Maybe it happens, maybe it doesn't. It is a 50/50 chance.

• "If I find your keys, I will tell you." (I might not find them!)

Use when when you are 100% sure the event will happen. It is for a certainty.

• "When the sun sets, it will get cold." (The sun always sets!)

Use this pattern for:

• Giving warnings: "If you touch that hot plate, you'll get burned."
• Making promises: "I'll help you with your bags when I finish this."
• Negotiations: "If you give me a discount, I'll buy two shirts."
• Directions: "When you see the big blue sign, turn left."

Don't use this for general truths or scientific facts. That is the Zero Conditional.

• Use: "If you heat ice, it melts." (This is always true, every time).
• Not: "If you heat ice, it will melt." (Though people might still understand you, it sounds a bit odd).

Don't use it for impossible or imaginary things.

• Don't say: "If I am an alien, I will fly to Mars."
• You aren't an alien. That needs the Second Conditional.

Also, don't use it for the past. This grammar only looks forward. It is a telescope, not a history book. If you are talking about yesterday, you are in the wrong neighborhood.

The biggest mistake is using will twice in the same sentence.

• Wrong: "If it will rain, I will stay home."
• Right: "If it rains, I will stay home."

Your brain wants to use will because it is the future. Resist the urge! The word if already does the heavy lifting for the future.

Another mistake is forgetting the -s for the third person (he/she/it).

• Wrong: "If he call, I'll answer."
• Right: "If he calls, I'll answer."

Yes, even native speakers mess this up when they are tired or rushing. Don't worry too much, just keep practicing until it feels natural.

Compare these two sentences closely:

1. 1"If I see him, I'll say hello." (Maybe I see him, maybe I don't).
2. 2"When I see him, I'll say hello." (I am definitely going to see him later today).

The grammar structure is exactly the same. However, the feeling is totally different. If is a question mark. When is an exclamation point.

Also, compare it with "Unless":

• "I'll go if it doesn't rain."
• "I'll go unless it rains."

Unless means "if not." It is like a grammar shortcut. It saves you a few syllables and makes you sound more like a pro.