There is another class of mental forms intimately connected with Psychology, and of this also we have denied the justification in the foregoing chapters, but only in the philosophical field, and not at all outside it. These are the _norms,_ or _normative_ knowledge and science, _maxims, rules, and precepts._ In truth, if philosophy, which commands and wills and judges, when its task is on the contrary to understand willing and commanding, and to make possible correct judgment--if such a philosophy be a contradiction in terms, there is yet nothing to prevent our taking the psychological classes, of which we have indicated the formation, and separating them from one another, according as they do or do not lead to certain other classes, which are called _ends_ and are _abstract ends._ This is done when those classes are selected which are more efficacious for practical action. Psychological classes and rules are therefore the same, save that in the second the character possessed by knowledge as prior to action is placed in relief, that is to say, its _technical_ character. This is proved by the easy convertibility of rules into psychological observations, and of the latter into the former. It suffices to add the imperative to the first and to remove it from the second. "Do everything so as to seem good, for that helps in many things; but since false opinions do not last, you will have difficulty in seeming good for a long period, if you are not so in reality." That is a rule of Francesco Guicciardini[1] (or rather of the father of Guicciardini, quoted by him). Now if we transfer this proposition from the imperative to the indicative mood and remove the predicate of exhortation, we have a mere psychological observation: "To seem good helps in an infinite number of things; but since false opinions do not last, it is difficult to seem good for long, unless one really be so." Here is a psychological observation of Vico upon seeming and being: "It happens naturally that man speaks of nothing but what he affects to be and is not."[2] This can be turned into a maxim: "Watch yourselves, in order that by talking too much of a given advantage, you may not let it be seen clearly that you do hot possess it." Or in relation to moral classes it can be turned thus: "Try to be that which you would like to appear to others," and so on. [Sidenote: _Usefulness of rules._]