In Chapter 7 of the Gita, Lord Krishna speaks of knowing God. It is hard to put the meaning of knowing God or knowing anything for that matter into words. But without a doubt, there are some things we know or at least we feel like we know.
I wonder what the difference is between thinking or feeling we know and actually knowing. I suppose the distinction only makes a difference when we speak of matters which others take seriously. To opine or feel or believe that we love someone is no different from loving someone. However, when it comes to science, or politics or faith, knowledge that does not conform to what others have confirmed or what our society may lead to dangerous action.
To know is not the same as to understand or to believe. Understanding and belief often lead to knowledge, but they are not knowledge itself.
Read more from The Gita at http://irinaspage.com/philosophy/the-gita-sacred/