 The philosophical view that emerges from the Ethics, in so far as it bears on physical theory, can be outlined as follows. God or Nature is the unique substance (Ip14), existing essentially (Ip7), infinite in power (Ip8), and characterized by infinite attributes, each constituting its essence (Id4). Finite things are but modifications of that substance, and not themselves independent beings (Ip14); bodies in particular are modes of substance conceived under the attribute Extension. God or Nature, as the ultimate cause of all things, is also the cause of all the particular modifications of extended nature (Ip18). However, substance's power is not expressed through the operations of will and intellect; the one substance does not act by conceiving a design in the intellect and bringing it to existence through the will (Ip23cl, Appendix, I). Hence Nature is not a teleological system, natural phenomena do not have purposes, and all causation between modes is efficient, none final. Since things are conceived through their causes, and modes are conceived always through the attribute to which they belong, there can be no trans-attribute causation. Bodies and their modifications cannot cause ideas, and ideas cannot cause modifications of bodies (IIp6). All modes are conceived through the substance in which they inhere; in this sense God or nature is an indwelling cause of all things (Ip18). But the particular modifications of Extension are causally necessitated entirely by the determining operation of prior modes of the same attribute, themselves so determined, ad infinitum (Ip28). The physical domain is thus completely closed causally, impervious to influence from modes of other attributes and to intervention of divine will, and fully deterministic (Ip29).