Introduction
Welcome back. In our previous lesson, we established the foundational principle of Go's opening strategy: prioritizing moves in the corners, then sides, and finally the center. You learned that this "corner, side, center" hierarchy is a direct consequence of efficiency—using the board's edges to claim territory with the fewest stones possible.
Now that you know where to play your initial stones, the next logical question is, "What do I do with them?" This lesson focuses on developing your corner positions. We will explore how to extend from these initial stones to achieve two critical goals mentioned in the learning outcome:
- Build a territorial framework: A large, influential area of the board with the potential to become your territory.
- Establish a base: A stable foundation for your group of stones, making it difficult for your opponent to attack and easy for you to make life.
By the end of this lesson, you will have a set of practical principles for expanding from your corners, turning a single stone into a powerful strategic asset.
From a Single Stone to a Corner Enclosure
After you've placed a stone in a corner, and your opponent has responded elsewhere, you often have the opportunity to play a second stone in the same corner. This is called a corner enclosure, or shimari in Japanese. Its purpose is to transform your initial investment into a more solid and secure position, firmly claiming the corner territory.
There are several ways to form an enclosure, each with a different character—some are conservative and safe, while others are more aggressive and open. The choice depends on your overall strategy and the position on the board.
The following video provides an excellent overview of the most common corner enclosures.
Go Opening Principles for the 19x19 Board - How to Start Strong
This clip from the Go Magic channel demonstrates the most common enclosures for the 3-4 point and the star point (4-4), explaining the strategic trade-offs between them.
Watch from 01:05 to 04:44. Pay attention to how different placements create enclosures that are either more secure (territory-focused) or more open and influential (framework-focused).
As the video showed, an enclosure from a 3-4 point is generally more secure than one from a 4-4 point, which often requires a third stone to fully lock down the corner territory. This is a recurring theme in Go: a trade-off between securing concrete points and building flexible influence.
Extending Along the Side: Frameworks and Bases
An enclosure solidifies a corner, but the game is won on a larger scale. The next step is to extend from your corner position along the side of the board. This is a key part of the opening, corresponding to Tiers 3 and 4 of the priority system we discussed previously. An extension serves two primary functions simultaneously:
- Building a Framework (Moyo): It stakes a claim to a large area of potential territory.
- Creating a Base: It gives your group stability and running room, making it much harder for your opponent to attack.
The Direction and Scale of Development
Not all extensions are created equal. A good extension works in harmony with your corner stones to efficiently outline a large potential territory. From an optimization perspective, you want to maximize the area controlled per stone played.
Let's see what this looks like in practice.
Go Opening Principles for the 19x19 Board - How to Start Strong
This next segment from the same Go Magic video illustrates the concept of building a large framework, or 'moyo'. It contrasts an inefficient, 'flat' development with an ambitious, 'box-like' structure that has far greater potential.
Watch from 04:44 to 07:52. The key insight here is that developing with height and space is vastly more efficient for creating large-scale potential than crawling along the third line.
This idea of building a "box-like" structure is central to developing a good territorial framework. Now, let's add more precision to this concept.
High vs. Low Moves: Territory vs. Influence
As you start extending, you'll face a fundamental choice: should you play on the 3rd line or the 4th line? This choice reflects a classic strategic trade-off in Go.
- Low moves (3rd line): These are territory-oriented. They create a smaller but more secure area. The 3rd line is often called the "line of territory."
- High moves (4th line): These are influence-oriented. They don't secure as much immediate territory but exert influence over a wider area of the board, contributing to a larger framework. The 4th line is the "line of influence."
A balanced opening often involves a combination of high and low moves.
Beginners guide to the opening at Sensei's Library
The Sensei's Library wiki offers a clear explanation of high vs. low moves and their strategic purpose. It's a fundamental concept for understanding how to build a balanced position.
Please read the section titled 'High moves and low moves'. Focus on the distinct purposes of 3rd-line and 4th-line stones.
How Far Can You Safely Extend?
You've chosen the direction and height of your extension. The final question is: how far can you jump from your existing stone or wall? If you extend too far, your opponent can cut through the gap. If you don't extend far enough, you are being inefficient.
Fortunately, there is a simple and powerful rule of thumb that governs safe extensions along the side.
This video from NYIG_Go provides a clear and practical rule for how far you can safely extend based on the number of stones you already have in your group.
Watch from 06:17 to 07:01, and then from 08:28 to 09:27. The first part introduces the concept of a two-space extension from a single stone as a good way to create a base. The second part generalizes this into a simple rule: a one-stone wall supports a two-space extension, a two-stone wall supports a three-space extension, and so on.
This is often summarized as the "N+1 rule": a stable wall of N stones along the side can support a safe extension of N+1 spaces.
- 1 stone -> 2-space extension
- 2 stones -> 3-space extension
- 3 stones -> 4-space extension
This rule is one of the most useful heuristics in the Go opening. It provides a reliable guide for creating stable, efficient formations. To solidify this principle, let's look at a classic written explanation.
Opening Strategy | British Go Association
This article from the British Go Association provides a concise explanation of this extension principle, showing diagrams of why these extensions are considered safe.
Read the section titled 'Extensions'. It formalizes the 'N+1' rule and shows through Diagrams 1-4 why an opponent's attempt to cut these extensions typically fails. This will reinforce the logic behind the rule.
Strategic Summary: The Economical Use of Stones
You now have a complete toolkit for developing your corner positions. You can form an enclosure to secure the corner, then make an extension along the side. You know to consider the direction (towards openness), the height (territory vs. influence), and the distance (the N+1 rule) of your extension.
These principles all serve a single strategic goal that should resonate with your background in economics: making the most economical use of your stones. In the opening, you are trying to stake out the largest possible area with the fewest moves, while ensuring your groups are stable. Every move is an investment, and these principles help you maximize your return.
The following reading summarizes this strategic outlook.
Opening Strategy | British Go Association
This final excerpt from the British Go Association article frames the principles of extension in terms of overall strategy and efficiency.
Read the final three paragraphs of the article, starting from 'The rule gives the maximum extensions possible...'. This section connects the tactical rules of extension to the broader strategic goals of maximizing area and using stones economically.
Conclusion
In this lesson, you've moved beyond simply placing a stone in a corner to understanding how to cultivate that stone into a powerful position. You now have the tools to build coherent territorial frameworks and establish stable bases for your groups, which is the heart of the Go opening.
Key Takeaways:
- Corner Enclosures (Shimari): Use a second stone to solidify your corner, choosing a shape that balances security and influence.
- Extensions: Play along the side from your corner position to build a territorial framework and establish a stable base.
- High vs. Low: Use the 4th line for influence and large frameworks; use the 3rd line for secure territory and stable bases. A good opening often combines both.
- The N+1 Rule: A wall of N stones can safely support an extension of N+1 spaces along the side. This is a crucial heuristic for efficient and safe development.
- Economic Play: All these principles aim to achieve the most economical use of your stones, maximizing your potential territory and influence with each move.
In the next lesson, we will enter the early middlegame. Once both you and your opponent have built frameworks and established positions, the board is no longer empty. The focus shifts to interaction: identifying and attacking your opponent's weak groups for profit, while defending your own.