Breathing is all‐important for survival, yet key aspects of the control system remain hidden from the gaze of consensus, not least the issue of central and peripheral chemoreceptor interaction. Activation (or inactivation) of either chemoreceptor alone will increase (or decrease) ventilation, but it remains unclear how the activation state of one chemoreceptor modality affects the chemoreflex response of the other (i.e., how inputs interact). Recent investigations consider three possibilities (e.g., Blain et. al., 2010; Cui et. al., 2012; Day and Wilson, 2009; Forster and Smith, 2012; Smith et. al., 2010; Tin et. al., 2012). Below, we consider four possibilities, three of which implicate some degree of hypoadditive interaction. This article is protected by copyright. All rights reserved.