First-Principles Reasoning
Reducing to physics, mathematics and economics, then reasoning up.
6 to work through
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beginner
A product manager asks for a 25 ms round-trip response time for users in London talking to a service in New York, arguing that a faster network provider would deliver it. Roughly what is the physical floor, and what does the answer let you do?
3 min answer -
intermediate
A vendor's datastore is documented at one million writes per second. Your cluster does 40000 writes per second and p99 write latency is 900 ms. Nothing is erroring. Work from first principles - where do the claim and your reality diverge?
2 min answer -
intermediate
An architect faces a problem that resembles a known pattern but does not quite fit. How should first-principles reasoning and pattern recognition be combined?
2 min answer -
advanced
A team says 200 ms is the minimum achievable latency for an operation. How would you check?
2 min answer -
advanced
When is first-principles reasoning the right tool for an architect, and when is it a waste of time?
2 min answer -
advanced
When should an architect reason from first principles and when should they pattern-match to known solutions? What goes wrong with each?
2 min answer
5 terms in this topic
Assumption Excavation
Deliberately surfacing the unstated beliefs behind a design or a requirement, to test which are constraints and which are merely habits.
practiceFirst Principles Thinking
Reasoning from what must be true rather than from what is usually done — the technique for problems where precedent is unavailable or misleading.
metricPhysical Latency Floor
The minimum achievable round-trip time between two locations set by propagation in fibre - roughly 1 ms per 100 km each way - which no provider, prot…
practicePrecondition Audit
Explicitly stating the conditions a pattern assumes and checking each against your situation - which is where pattern matching becomes judgement rath…
practicePrecondition Check
Testing whether a problem's conditions match the assumptions a familiar pattern encodes - the ten-minute exercise that separates useful pattern reuse…
Neighbouring topics
Meta-Skills
General material on how architects think and work.
Systems Thinking
Interactions and feedback loops rather than isolated components.
Trade-off Analysis
Making costs explicit and comparable rather than asserting a preference.
Failure Thinking
Asking of every box and arrow how it fails and how you would know.
Constraint Thinking
Designing for the budget, skills and regulations that actually exist.
Pattern Recognition
Seeing a familiar problem, and checking whether the forces match.
Pragmatism
The simplest architecture that meets the requirements usually wins.
Judgement Under Uncertainty
Choosing the best worst case when information is missing.
Business Understanding
Connecting a design to the outcome that pays for it.
Influence Without Authority
Getting decisions adopted when you cannot mandate them.
Mentoring
Growing architectural judgement in other people.
Continuous Learning
Staying current without chasing every new thing.
Estimation
Sizing work and cost honestly, with the uncertainty stated.
Prioritisation
Choosing what not to do, and defending it.
Research & Evaluation
Assessing a technology quickly without adopting it by accident.
Handling Ambiguity
Making progress when the requirements are not yet knowable.
Technical Leadership
Setting direction and carrying accountability without a team reporting to you.
Ethics in Architecture
Privacy, accessibility, sustainability and the consequences of a design.
Career Development
Growing from senior engineer to architect and beyond.