In this type 1 first conditional, the simple present tense is used in the if-clause, and the tense in the main clause is the simple future tense.
|'If' Clause||Main Clause|
|If + simple present tense||Simple future tense|
|If you leave now,||you'll arrive home early.|
This conditional shows the outcome (you’ll arrive home early) if the condition is fulfilled (if you leave now). We use this conditional when the situation in the if-clause appears likely or there is a possibility of it happening.
We can turn the two clauses the other way round so that their positions are reversed as follow:
|Simple future tense||if + simple present tense|
|You'll arrive home early,||if you leave now.|
Whether the if-clause or the main clause comes earlier, both are acceptable.
The first conditional sets up a present condition and a probable future outcome.
We may use going to in the first conditional to refer to a future event.
First conditional and modal verb.
Modal verbs may be used in the first conditional. The modal verbs have a future meaning and so are used instead of the future tense in the main clause, not in the conditional clause.
|Conditional Clause||Main Clause|
|If + simple present tense||can/could; will/would; may/might; shall/should|
|If the weather improves,||we will go to the park.|
The modal verbs are used in type 1 conditional sentences to express willingness, possibility, permission, and suggestion.