Zero conditional = general and scientific truth (if + present / present). First conditional = possible and realistic future situation (if + present / will + infinitive).
ZERO CONDITIONAL: IF + SIMPLE PRESENT / SIMPLE PRESENT. Expresses general truths, laws of nature, scientific facts, or situations that ALWAYS happen when the condition is met. The result is INVARIABLE and predictable. "If you heat water to 100°C, it boils" = always true. "If it rains, the ground gets wet" = general truth. "If you eat too much sugar, you gain weight" = habitual consequence. Both condition and result are certain: no probability, only cause and effect.
If you do not back up your data regularly, you lose important files the moment your hard drive fails.
If the team misses deadlines consistently, client trust erodes and contracts become harder to renew.
If demand exceeds supply, prices go up — that is a basic principle of market economics.
FIRST CONDITIONAL: IF + SIMPLE PRESENT / WILL + INFINITIVE. Expresses a future situation the speaker considers POSSIBLE or LIKELY (not merely theoretical). "If it rains tomorrow, we will cancel the picnic" = it may realistically rain. "If she passes the exam, she will celebrate." The WILL result indicates a FUTURE consequence the speaker genuinely anticipates. The condition is not certain (may or may not happen), but the probability is perceived as real.
If the board approves the budget next week, we will start the hiring process for the new engineering positions immediately.
If she finishes the prototype before the end of the month, the team will present it at the investor meeting in April.
If the weather is good this weekend, we will hold the team-building event outdoors in the park.
Common mistake
Most common error: using WILL in the IF clause. "If it WILL rain, we will cancel" = INCORRECT. The IF clause ALWAYS uses SIMPLE PRESENT, not future: "If it RAINS, we will cancel." This error is made by speakers of many languages. In English, future (will/going to) NEVER goes in the conditional IF clause of zero or first conditional. Second error: confusing zero and first conditional by context. "If you press this button, the machine stops" (zero = always happens, general truth). "If you press this button, the machine will stop" (first = in this specific future situation, it will happen).
Trick to remember it
The TWO PARTS rule: IF clause (condition) + main clause (result). Zero: IF + PRESENT / PRESENT. First: IF + PRESENT / WILL. The IF clause NEVER uses "will". To choose between zero and first: ask — is it ALWAYS true (law, habit, science)? = ZERO. Is it something that COULD REALISTICALLY HAPPEN in the future? = FIRST. "If you mix blue and yellow, you get green" = zero (always true). "If you mix these chemicals incorrectly tomorrow, you will create a toxic reaction" = first (specific possible future situation).
Quick rule
Zero conditional: if + present / present (always-true facts). First conditional: if + present / will + infinitive (possible and realistic future situations). The IF clause never takes "will" in either type.
Did you know?
English conditionals have a system of four types (0, 1, 2, 3 — and sometimes a "mixed" type) that textbooks number as if they were completely distinct, but which in reality form a continuous spectrum of probability: from 0 (absolute certainty) to 3 (past impossibility). Modern linguists prefer to speak of "real conditionals" (zero and first) and "unreal conditionals" (second and third) rather than numbering them. Interestingly, the grammatical distinction between zero and first conditional does not exist in Spanish: "si llueve, nos mojamos" can be both a general truth and a future situation — English forces the speaker to be explicit about the nature of the condition.
Exercise 1 · Pick the right one
If you _____ enough sleep consistently, your cognitive performance _____ significantly.
Exercise 2 · Pick the right one
If the client _____ the revised proposal by Friday, we _____ the project launch to Q4.
Exercise 3 · Form the word
Zero conditional: if + present / present (always-true facts). First conditional: if + present / will + infinitive (possible and realistic future situations). The IF clause never takes "will" in either type.
Most common error: using WILL in the IF clause. "If it WILL rain, we will cancel" = INCORRECT. The IF clause ALWAYS uses SIMPLE PRESENT, not future: "If it RAINS, we will cancel." This error is made by speakers of many languages. In English, future (will/going to) NEVER goes in the conditional IF clause of zero or first conditional. Second error: confusing zero and first conditional by context. "If you press this button, the machine stops" (zero = always happens, general truth). "If you press this button, the machine will stop" (first = in this specific future situation, it will happen).
The TWO PARTS rule: IF clause (condition) + main clause (result). Zero: IF + PRESENT / PRESENT. First: IF + PRESENT / WILL. The IF clause NEVER uses "will". To choose between zero and first: ask — is it ALWAYS true (law, habit, science)? = ZERO. Is it something that COULD REALISTICALLY HAPPEN in the future? = FIRST. "If you mix blue and yellow, you get green" = zero (always true). "If you mix these chemicals incorrectly tomorrow, you will create a toxic reaction" = first (specific possible future situation).
Bryan López
Founder of SpeakUP Academy