Skill Trees

Tim's Games: Linear Skill Systems

Most of Tim Cain's shipped games feature relatively linear skill progression. You get a set of skills, earn points as you level up, and spend them to make skills incrementally better. Variations include:

• Arcanum — players could acquire named ranks within skills
• The Outer Worlds — early on, players could only invest in broad skill categories (e.g., "Dialogue"). Once 50 points were invested, individual sub-skills unlocked (Persuade, Lie, Intimidate), each usable in specific game contexts

Tim calls The Outer Worlds' approach "very short skill trees — maybe skill bushes." The category-then-specialization model is a mild form of prerequisite gating that still keeps things approachable.

Shapes as Design Tools

Tim identifies three common structural shapes for skill systems:

• Trees — branching paths with clear parent-child prerequisites
• Graphs — interconnected webs of skills (Path of Exile being the extreme example)
• Matrices — grid-based layouts where rows and columns create structure

All of these are ways to constrain player choices — each skill you pick determines what you can pick next, either through direct prerequisites or point thresholds. Tim notes that this constraint is visually intuitive: a grayed-out skill pointing to a prerequisite is something players immediately understand.

Sidebar: People Understand Shapes

Tim emphasizes that humans naturally understand spatial relationships, which is why visual skill layouts work so well. He has wanted to design a "shape-based attribute system" for years but hasn't figured out how to make it work yet — though he hasn't given up, noting that it took him years to figure out how to introduce flaws mid-game (which eventually shipped in The Outer Worlds).

Fallout: A Missed Opportunity

If Tim were to remake Fallout, he would at minimum let players see all perks from the start. In the original game, perks had prerequisites but players couldn't view perks until they were offered. Showing the full perk landscape — with prerequisite links visible — would let players plan their builds across the entire game, which is something players love to do, especially on repeat playthroughs.

The Epic Ability Matrix (2004)

Tim's most detailed skill system design was for Epic, a cancelled post-apocalyptic RPG at Troika Games, designed around 2004. It used what he called an "ability matrix" — essentially a grid with four primary columns and crossover columns between them.

Four Primary Categories

Each category contained a deep linear list of abilities, progressing from basic to powerful:

1. Social — dialogue and interpersonal abilities
2. Thieving — stealth, lockpicking, pickpocketing (progressing from "pick simple lock" up to "disappear from view")
3. Combat — melee and weapon abilities (starting with "melee thrust")
4. Magic — spells and supernatural abilities

Crossover Categories

The innovative part: between each pair of adjacent primary categories sat a crossover column containing hybrid abilities drawing from both neighbors:

• Social–Thieving crossover: Bluffing, Disguise
• Thieving–Combat crossover: Sneak Attack
• Combat–Magic crossover: Cloud Mind (a spell that made opponents slower and less perceptive — useful for combat and thievery alike)

Notably, non-adjacent categories (Combat–Social, Thieving–Magic) had no direct crossover — but players could reach them by hopping through intermediate crossover columns.

Character Creation and Progression

The game featured three-phase backgrounds — birth, childhood, and adolescence — that determined which primary categories a player started with. For example, a character born as a barbarian who ran with a street gang in adolescence would start with access to Thieving and Combat columns.

Each level-up offered a choice: pick the next ability in a primary column, or pick from an adjacent crossover column. This created organic lateral movement:

• A Thief–Combat character who wanted magic could pick Cloud Mind (Combat–Magic crossover), then at the next level enter the Magic column directly
• A Thief who wanted social skills could pick Bluffing (Social–Thieving crossover), then transition into the Social column

Generalists vs. Specialists

The matrix structure naturally supported both playstyles:

• Specialists could deep-dive down a single column, gaining increasingly powerful category-specific abilities
• Generalists could spread across multiple columns via crossovers, collecting low-level abilities from many domains

Each ability in a column provided either increased power, expanded variety (what you could target), or improved frequency (how often you could use it).

Design Takeaways

The shape of a skill system isn't just cosmetic — it's a fundamental design decision that determines:

• What character archetypes are possible
• How much players can plan ahead
• Whether hybrid builds feel natural or forced
• How much the system guides vs. constrains the player

Tim's matrix design for Epic remains one of his most ambitious skill system concepts, blending the clarity of linear progression with the flexibility of a graph through its crossover mechanic.