That is when we go you His Word, which He promised would never fade by the way, and make sure you are lining up with His word. His Spirit leads us to all truth, and I have to add it's a bit strange for a Christian to ask "How do you know it it's the Holy Spirit or just you", do you not understand this? Is it not something you deal with every day since salvation. I say how can you NOT know it's the Holy Spirit? Not that I'm saying we can figure out everything without looking into it, but if it's His Spirit it WILL lead you to all truth.