To return to the question of method. Rossi made use of an ingenious example to explain his thought:(44) “Are,” he inquires, “these deductions [of pure science] perfectly legitimate; are these consequences always true? It is incontestably true that a projectile, discharged at a certain angle, will describe a certain curve; this is a mathematical truth. It is equally true, that the resistance offered to the projectile by the medium through which it moves modifies the speculative result in practice, to some extent; this is a truth of observation. Is the mathematical deduction false? By no means; but it supposes a vacuum. I hasten to acknowledge it. Speculative economy also neglects certain facts and leaves certain resistances out of account.” Now, from the moment that we have to deal with human interests, it is not possible to suppose a vacuum, to neglect the most vulgar facts, and the most common instances of resistance, nor to lose one’s self in abstraction. The correctives of applied Political Economy either may not wipe out this original sin, or else they run great danger of covering up the principles themselves. In ballistics, again, we may measure the resistance which the medium in which we are obliged to operate, makes the force of impulsion and the target both obey the same law, and yield to the same process of calculation. But is it thus when you touch upon man’s innermost and most sensitive part? Is there not danger that the hypotheses may be deceitful, and that you may be accused of toiling in a vacuum? We well know the solid reason that may be opposed to sarcasm of this nature; but is it expedient to lay one’s self open to it? Moreover, the consequences are not great enough to warrant us to expose ourselves to the danger. The principles of pure science are very small in number. They might even, be easily reduced to one, of which M. Cousin has been the eloquent interpreter—human liberty. This liberty has no need of Political Economy to shine with the luster of evidence; nothing can prevail against it. We can prove that it is as fecund as it is respectable; but if the science of wealth should endeavor to demonstrate the contrary, the primordial bases of society, liberty, property and the family would not be less sacred nor less necessary, for they are the right of humanity. They could not be put aside, even under pretext of any mechanism which would claim to produce more.(45) These sovereign principles of economy flow from the moral law, and they have no reason to dread the power of facts, for the prosperity of nations depends on the respect with which they are surrounded and the guarantees by which they are protected.