While micro-variation, i.e. variation between dialects or among speakers, has been established and proven in recent years as a research discipline in its own right in (also theoretically informed) linguistics, variation within a speaker that cannot be attributed to sociolinguistic variables has, so far, hardly been studied. We call this form of variation – the occurrence of two different structural options for one function – ‘optionality’. We focus on optionality in syntax and identify at least two different types of optionality: while context or co-text plays a role in the first type, neither constraint seems to be relevant to the choice of one option or the other in the second type.