First conditional:
very likely (waarschijnlijk)
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If you do A, then B will happen.
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if + subject + present simple, subject + will + verb
If I cross a red light, I will get a ticket.
Second conditional:
unlikely (onwaarschijnlijk)
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If A were true, B would be true.
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If + subject + were, subject + would + verb
If you weren't coming to the party, I also wouldn't go.