This paper discusses two of the established tenets in paper conservation that permeate the existing relevant literature and define the conservation practice, in the light of recent findings. The idea that washing and deacidification can only be beneficial and that effects on ink and colours excluded, there are no negative side effects to paper properties, has been openly expressed and supported in many publications. New research and scattered uncommented results in the relevant literature though indicate that aqueous treatments may have a detrimental effect on the mechanical properties of paper, especially tensile strength and folding endurance. It is suggested that according to the principle of minimum intervention, washing and deacidification should be applied to acidic paper, and then followed by consolidation. Another tenet with important implications on conservation and preservation decision making concerns the rate of ageing. Research based exclusively on accelerated ageing tests has shown that ageing is at first a linear process which decelerates after a certain point. Nevertheless, the applicability of this scheme to the natural process of paper ageing has been argued, and another model based on accelerated ageing tests done in closed environments has been proposed which is believed to simulate natural ageing better than the previous one. In the early stages of ageing, both models give similar results, but overall, the linear model dramatically overestimates the useful life of paper. The newer model indicates that natural paper ageing in libraries and archives can be an accelerating process and puts to question the foundations of conservation research and preservation practice.