Five experiments demonstrate that context has a powerful effect on the ease with which people can name (Experiments 1-3) or categorize (Experiments 4-5) a stimulus while ignoring another stimulus, irrelevant or conflicting with the target. Selectivity of attention to the target dimension was gauged through Stroop and Garner effects. When the stimulus values along the target dimension and the to-be-ignored dimension were correlated over the experimental trials, large effects of Stroop and Garner influenced performance. However, when random allocation of values created zero dimensional correlation, the Stroop effects vanished. These results imply that when the nominally irrelevant dimension is in fact correlated with the relevant dimension, participants then attend to the irrelevant dimension and thus open themselves up to Stroop interference. Another variable of context, the relative salience of the constituent dimensions, also affected performance with the more discriminable dimension disrupting selective attention to the less discriminable dimension. The results demonstrate the importance of context in engendering the failure of selective attention and challenge traditional automaticity accounts of the Stroop effect.