World 3: Parallel Universes

Three-way merge

You will learn: how Git joins two branches that both moved on.

The problem

~/diary $ git log --oneline --graph --all* 01bb13d (HEAD -> main) Make heading teal| * 203a91f (about) Say what I like| * a20da6c Add about page|/  * 270a76e Add style* a8feb63 Add day 1 page* 6d3a9b1 Add README

This time main moved on too. The note can’t just slide forward. What will Git do?

Watch

Git makes a new . It has two parents, one from each branch. Both stories join here.

Try it

Git compares three commits: your tip, their tip, and where they split. That spot is the . Find it.

Tap the last commit both branches share.

Watch

~/diary $ git merge aboutMerge made by the 'ort' strategy. about.html | 2 ++ 1 file changed, 2 insertions(+) create mode 100644 about.html

Base, yours and theirs: three commits go in. That’s a . The word ort is the name of Git’s merge engine.

Try it

Your turn. You are on main. Merge about.

Hint

Type git merge about, then press Enter.

Predict

How many parents does a merge commit have?

Check

Fast-forward, or a new merge commit?

Drag a card into a box. Or tap the card, then tap the box.

You did it!

You can now merge branches that both moved on.

Go deeper (optional)

git show on a merge commit prints a Merge: line with both parents. git log --merges lists only merge commits. Git suggests the message Merge branch ‘about’. In a real terminal, your editor opens with it ready.

~/diary $ git merge aboutMerge made by the 'ort' strategy. about.html | 2 ++ 1 file changed, 2 insertions(+) create mode 100644 about.html~/diary $ git show HEADcommit 5a96d9e9064ee58d8f1105924df833a83948d2cf (HEAD -> main)Merge: 01bb13d 203a91fAuthor: You <you@example.com>Date:   Fri Oct 30 09:07:00 2026 +0800    Merge branch 'about'