An invention is the most straightforward kind of patent in regards to establishing its patentability – a typical utility patent is often some kind of invention, after all, and very commonly it is a mechanical invention of the sort familiar to all of us – an engine, a lightbulb, a new kind of tool, etc. Thus an invention is clear cut in its requirements for patentability, so long as you meet the requirements of patent utility, novelty and non-obviousness.