Sustainable development in its literal meaning as a strategy which depends on renewable resources cannot be attained for the present global energy needs. A more realistic goal, the concept of constant time of safe practice, is proposed according to which the time into the future should not decrease during which the actual strategy of development (as given by the overall policy regarding population growth, energy, economy, land use, et cetera) can be guaranteed – to the best of our knowledge – as being safe and sustainable. Since every mode of energy supply, whether from renewable sources or not, limits the society's option to some extent, it is proposed to put an absolute limit to the level of energy use. The principle of energy bounds is meant as an alternative to the method of energy taxation. The former addresses directly the ultimate goal to reduce our energy dependence while the latter, due to adjustment of the energy needs to the new prices, may not be the adequate tool to bring about, in the long run, a smaller rate of energy degradation.