Relative clauses — defining and non-definingEssential information, and information added in passing.Related learning areasEnglish GrammarRelated conceptsAbility and possibility — can, could, be able toArticles — a, an, the, and no articleChoosing between comparatives and superlativesChoosing between conditionalsChoosing between gerunds and infinitivesFirst conditional and future time clausesQuestionsAll questions in this subjectStart learningStart free practice