Bluetooth—so simple and yet so troublesome. For a subsection of users, Yosemite is causing problems with Bluetooth accessories and connectivity. One solution proffered by iDigitalTimes is to disconnect all USB preferences, shut the Mac off for several minutes and then try again from the beginning. You may have to teach Yosemite about your Bluetooth accessories afresh instead of relying on what Mavericks has passed on. Over on the official Apple forums, it looks like resetting your machine's PRAM (Parameter Random Access Memory) once or twice might fix the problem. PRAM is where all of the core information about your system is stored, and you reset it by booting up, then holding down the Cmd+Option+P+R keys right after you've hit the power button. When you hear the startup sound for the second time, you can let go.

We obtain the concept, as we do the form, by overlooking what is individual and actual; whereas nature is acquainted with no forms and no concepts, and likewise with no species, but only with an X which remains inaccessible and undefinable for us.