Each person views the world through a unique lens. This, in turn, affects the manner in which each of us interacts with our environment. Ever since I can remember, I have always enjoyed activities that allowed for a great degree of variation while still imposing a distinct set of restrictions. I was never really into jigsaw puzzles, on the one hand, because there is only one correct solution. Painting, on the other hand, allows for too many possibilities since it imposes no restrictions beyond the two-dimensional canvas and the imagination of the artist. My favourite childhood toy was Lego: a large box of Lego pieces allowed for a huge set of possible outcomes while still very much restricting the builder to a set of basic shapes and mechanisms for interconnection. This same Lego-block style of thinking is what ultimately lead me to a career in engineering and is also a key reason that I enjoy Magic: the Gathering.
Building a Magic deck of any variation - whether it be Constructed, Sealed, Draft, Commander or whatever - requires the builder to select from a set number of pieces - the cards - and build a deck within some basic restrictions - deck size, number of copies of each card, etc. The card pool from which one may choose is effectively their box of Lego pieces. This may be defined by the format - Standard, Modern, Legacy, etc. - or simply by the cards physically on hand, as in the case of Limited formats. The resulting deck represents the builder's unique perspective exerted upon the Magic environment.
The concept of a box of Lego pieces has slowly developed within the Magic community not only into Limited formats, but over the past few years also into the concept of a cube. At its most basic level, a cube is simply a box of Magic cards that you use to build decks. The box could contain anything, such as the cumulative collection of cards obtained from past five years of pre-release events, for example. But it is human nature to exert one's will on the environment. Cube owners do this by selecting the cards that are contained in the box. Thus, cube design was born.
If you have followed some of the history of cube, from Sam Gomersall and Tom Lapille to Evan Erwin and Thea Steele and many others, then you're probably very familiar with the standard definition of cube as a collection of the most powerful cards in Magic's history stuffed together into a set to be drafted. To my engineering mind, this is simply a group of people agreeing on a basic design criteria: the cards in the box are selected because they're the best cards in the history of Magic. It is, indeed, a fine criteria for selection. In fact, whole cube communities have developed (such as this one at mtgsalvation.com) in which like-minded individuals gather to discuss exactly which cards should be included in a cube. Further, Wizards of the Coast has chosen to surf the wave of cube enthusiasm both by creating a cube that can be drafted on Magic Online, as well as recently featuring cube draft as an official format at the Magic Players Championship. This official support further cements the common understanding of what a cube represents. I have built such a cube myself, and have learned a great deal about cube design from the various cube communities and authors on the subject.
In the process of cube construction, I have come to realise that restricting the criteria for cube design only to the "best" cards has its own caveats and limitations. For one thing, it's difficult to get agreement on which cards, exactly, are the most powerful. Cube lists differ even among those who subscribe to this basic definition. There are those who for various reasons have decided to exclude the "power 9" cards - the most powerful and, generally speaking, most expensive cards ever printed. Some cube designers restrict the sets from which cards are considered acceptable for inclusion, excluding, for example, cards from the un-sets (Unglued, Unhinged) and sometimes from sets such as Portal which were never part of any official format. Most cube designers also make some attempt to give structure to their cube by balancing the five colours, artifacts, multi-coloured cards and lands. This is like choosing how many blocks of each colour will be in the box of Lego. Furthermore, experience with playing the cube has lead many cube builders to include selections that support various deck archetypes in order to create a more varied and balanced play environment. This also helps to create linkages between the pieces, much like selecting styles of Lego, such as Lego Castle or Lego City. However, every time a card is included for one of these reasons it is potentially replacing a card that is "better". As a result, there is already far more to a cube than simply being the best cards, even if this remains the primary design principle.
Upon further inspection, however, it becomes apparent that this is not the only possible design criteria. "Pauper" cubes refer to those built using only common cards; "Peasant" cubes are built using only common and uncommon cards. Generally these cubes are still applying the "best of" criteria, but only within their overarching restriction on card rarity. There is also the concept of Block cubes. These cubes are different in the sense that there really isn't any design involved; rather, they contain one copy of every card in a Block of sets as released by Wizards of the Coast. I have put together a couple of these myself: I have a complete set of Innistrad and a complete set of Dark Ascension in a box ready to be drafted. It is also possible to cross the concepts: I have a Block cube which is simply every common and uncommon in Scars of Mirrodin Block and another which is every common and uncommon in Innistrad Block (including Avacyn Restored). While there is no design involved in these cubes, they do provide a very good approximation of what it feels like to draft the entire set and get a feel for the various mechanics and interactions.
There are also "themed" cubes which attempt to build a cube based around some criteria other than "the best cards". A common example is a Tribal cube, which promotes drafting decks around a particular creature type. Themed cubes tend to get less attention within the cube communities. The primary reason for this seems to be that when a cube designer is building along some axis other than "the best", other cube designers find it difficult to provide input. This makes sense, but does not reduce the value of such cubes. In fact, this is probably the area of greatest interest to me currently - not so much designing a cube around a specific theme such as Tribal, but simply designing a cube which is a set all on its own, with cards chosen specifically for their fit within that specific environment.
Cube design provides an opportunity to design and build a Magic set of my own, using the pieces provided by Wizards of the Coast. The result of my effort, in turn, is a box of pieces to be used by myself and my friends to form our own creations. Cube design, for me, is the study and application of the various criteria for defining what is to be included in my box of cards, whether this be the structure, archetypes, mana curves, colour pie breakdown, individual card selection or any other criteria.
So, while it is common to refer to a cube as a collection of the best Magic cards of all time, I will also continue to explore the various facets of custom draft set design which represents the greater hobby that is cube design.