Sake has a reputation as being difficult to understand. However, in truth, getting to grips with the basics is actually easier in comparison to other beverages. For example, whereas the quality of wine is greatly dependent on the raw ingredients, that of sake is largely determined by the production method. Moreover, this production method can often be what separates the different classifications. Therefore, in order to understand the basics, one must simply learn just seven simple categories that make up the sake family tree.
The pyramid below details these various different categories, from regular sake (futsushu) at the bottom, to ultra-premium (daiginjo) at the top. With the exception of futsushu, the most significant factor legally separating all of the grades is the level of rice polishing. However, others include the amount of additional alcohol that's permitted to be added, and the use of additional flavorings. Finally, although not legally binding, the premium categories, in particular ginjo and daiginjo, will more often that not be brewed using more careful labour intensive methods. Specifically, orthodox ginjo production calls for fermenting at cooler temperatures for a longer period of time.
Outside of this, the sake family tree is divided between junmai types, meaning "pure rice", and aruten types. Whereas junmai types have no added alcohol, aruten have had a small amount added to enhance flavours and aromas. Indeed the name is a combination of the words arukouru (アルコール) meaning alcohol and tenka (添加) meaning "to add" in Japanese. Neither variation is superior in quality in comparison to the other, just a little different. However, in general, selecting sake based purely on the typical characteristic of these classifications is not always a sure-fire guarantee you will get what you are expecting. There is much crossover between them, and many examples will not conform to the status-quo of that particular classification.
It is also worth noting that, although the premium categories are very often made with the upmost care and attention, it does not necessarily mean that everyone will automatically prefer these grades over the lower categories. They each have their own merits and should all be explored with an open-mind. However, what is good to know is that there exits a huge amount of diversity amongst sake, and there is a style for virtually all occasions. So its definitely worth learning the categories below, but don't get overly hung-up on them. As always, the most important thing is to keep an open-mind.
For a more detailed explanation of the various grades, please follow the link to my blog entitled The Basics: Beginners Guide to Sake Classifications