premise: Even the remnants we have from early languages that had a writing system are relatively  Classical Latin and Greek, Hebrew, and a few other languages are better documented than others; but for most all we have to go on are a handful of tablets here, a few inscriptions there, barely enough in many cases to allow us to identify the language, let alone draw any conclusions regarding its structure or meaning.
hypothesis: We can only rely on tablets, which are not enough to draw conclusions regarding language structure and meaning.