A _third_ requisite for beauty is that the object be in itself _duly proportioned_, _orderly_, _well arranged_. _Order_ generally may be defined as right or proper arrangement. We can see in things a twofold order, _dynamic_, or that of _subordination_, and _static_, or that of _co-ordination_: the right arrangement of means towards ends, and the right arrangement of parts in a whole, or members in a system. The former indicates the influence of _final_ causes and expresses primarily the _goodness_ of things. The latter is determined by the _formal_ causes of things and expresses primarily their _beauty_. The order essential to beauty consists in this, that the manifold and distinct things or acts which contribute to it must form one whole. Hence order has been defined as _unity in variety_: _unitas in varietate_; variety being the material cause, and unity the formal cause, of order. But we can apprehend unity in a variety of things only on condition that they are _arranged_, _i.e._ that they show forth clearly to the mind a set of mutual relations which can be easily grasped. Why is it that things mutually related to one another in one way make up what we declare to be a chaotic jumble, while if related in another way we declare them to be orderly? Because unless these relations present themselves in a certain way they will fail to unify the manifold for us. We have an intellectual intuition of the numerical series; and of _proportion_, which is equality of numerical relations. In the domains of magnitude and multitude the mind naturally seeks to detect these proportions. So also in the domains of sensible qualities, such as sounds and colours, we have an analogous intuition of a qualitative series, and we naturally try to detect _harmony_, which is the gradation of qualitative relations in this series. The detection of _proportion_ and _harmony_ in a _variety_ of things pleases us, because we are thus enabled to grasp the manifold as exhibiting _unity_; while the absence of these elements leaves us with the dissatisfied feeling of something wanting. Whether this be because order in things is the expression of an intelligent will, of purpose and design, and therefore calls forth our intelligent and volitional activity, with its consequent and connatural feeling of satisfaction, we do not inquire here. But certain it is that order is essential to beauty, that esthetic pleasure springs only from the contemplation of proportion and harmony, which give unity to variety.(204) And the explanation of this is not far to seek. For the full and vigorous exercise of contemplative activity we need objective variety. Whatever lacks variety, and stimulates us in one uniform manner, becomes monotonous and causes _ennui_. While on the other hand mere multiplicity distracts the mind, disperses and weakens attention, and begets fatigue. We must, therefore, have variety, but variety combined