Jacques Derrida (Post Lecture)

I had never had the pleasure of having heard a lecture by Professor Casey. Unfortunately, last time he visited I missed class due to not feeling well, but luckily I was feeling great and ready to learn this time. I would like to bring up a few of the concepts he explained about Jacques Derrida.
He stated that Jacques Derrida's underlying principle is logocentrism, which we defined as logo meaning word and centrism as central. The word is at the beginning of it all. In the beginning of the lecture we were asked to look at the word Hell, then a symbol of the shell gas station, the the word S ELL, and then again Hell. These examples proved that in a short span of time, one signifier changes after relation to other signifiers. Then we looked at Derrida's notion of 'the trace', which I took note as synaptic ideas in our brain (once we see it, we can never go back). The example given was the etch-a-scketh, where if you leave a particular scketch on it, then try to erase it, it leaves a trace of that particular picture you can never get rid of. A great quote about the trace by Derrida was "you cannot escape this concept," he is saying you cannot get outside of ideology, the trace is always working on you.
We also learned about his concepts of Erasure, and Difference/Differance and Alterity.
Prior to the lecture I was unsure of what Derrida's ideas and concepts were, after the class I feel confident in my knowledge of his concepts and I can even relate him to other theorists.