A posteriori does not exist as memory is a thought process. You cannot communicate or even remember anything without thinking first and so therefore the only method of knowledge and understanding must be a priori. You cannot claim that a car is green or you have just gone to the toilet as you have had to process the concept of a red car and going to the toilet before you can realise that you have experienced these. Of course you can claim that a posteriori knowledge and a priori knowledge are merely distinctions between inference and fact, but by definition posteriori can only exist if we happen to be omnipotent and do not require physical processes in order to perceive and remember. You can claim that we are sentient and that is supernatural enough, however if you were to perform experiments on your brain, you would seee that your sentient self is affected. This implies that despite the fact you are sentient, you are still under the dictate of physical processes, a posteriori does not exist and a priori is the process in which all knowledge is attained. Examples. You are currently perceiving a red flower. If you were to sever your optic nerves you would stop perceiving a red flower, this is because a process was involved that involved processing the image and realising that it is a red flower. The examples can get even simpler. You claim that the activation of a nerve next to a part of the brainthat will make you perceive something is a posteriori as the processes involved are so simple that they cannot possible be a priori. You infer that you are perceiving something, the detection of this sensation is a priori. Of course you can also claim that everything is a posteriori as the 'circuits' that define our brains are themselves 'sensing' each other directly, though again, by definition no matter how simple the mathematics involved in perception and thought all knowledge must be a priori.