Reasoning: Inductive, Deductive & Abductive Reasoning

Research relies on reasoning. During the research process, we use methods to produce data. But data just sits there. It doesn’t do much (like Perry the Platypus) until we apply reason to make sense of it. That’s where inductive, deductive, and abductive reasoning comes in. Each of these types of reasoning has its place. You have to know when and where to use them.

Reasoning Basics and Design

When designing and especially researching for design, you will use different ways of reasoning to figure out what’s going on and what to make. We’ll use design scenarios to break different types of reasoning down, so they make more sense for our use.

Deductive Reasoning

Deductive reasoning starts with a conclusion (premise), then finds evidence to support that conclusion. People refer to this as “top-down” logic. If you already know what matters but want to find out why it matters or what caused it, then use deductive reasoning. Here’s a scenario:

What we know: Twenty One Pilots is performing at American Airlines Center right now.

What we observe: Traffic downtown is awful. Ticket scalpers are selling tickets on street corners.

What we conclude: The concert is the reason why congestion is so bad.

What we can do about it: Maybe we could design better traffic flow, so congestion is reduced.

Inductive Reasoning

Inductive reasoning is pretty much the opposite of deductive reasoning. When we reason inductively, we start with what we observe and then conclude based on those observations. Inductive reasoning is “bottom-up”—it starts with little bits of information, and a conclusion follows from that information. Here’s another scenario:

What we observe: Tables in a Thai restaurant have not been cleared. Glasses, plates, and half-eaten settings are on most of the tables in the room. Customers at a few tables look disgruntled and are looking around for someone. A server is sitting on a chair in the back of the room using a smartphone.

What we conclude: The server must not be paying attention to their job. They are more interested in their phone than they are in doing their work.

What we can do about it: We can design policies for on-duty employee smartphone use. We can hire employees who are dedicated to creating a great restaurant experience for guests.

Here’s an inductive reasoning caveat: by definition, inductive reasoning should arrive at a certain, verifiable, and 100% certain conclusion. For example, if we measured 10 ml of a mineral powder then mixed it with water to produce yellow smoke, we could reason that the mixture produced it. We could test this 100 times and produce the same result to ensure that our reasoning was sound.

The spirit of inductive reasoning is perfect for design. However, designers seldom work in a world of certainty because the things we make involve people. We can’t perfectly measure how much a person likes Instagram posts using milliliters or grams. So, we use abductive reasoning to make conclusions.

Abductive Reasoning

Abductive reasoning is like inductive reasoning in that it starts with observations and produces conclusions that come from those observations. However, abductive reasoning doesn’t produce 100% correct conclusions—it produces the most likely conclusion based on available information. Sherlock Holmes is known for being a master of deduction, but actually, he uses abductive reasoning to arrive at conclusions.

Sherlock notices everything around him. He surveys what’s going on and notices all of the evidence—then he puts it all together with reason. He arrives at the most likely conclusion based on observable evidence, though it’s not guaranteed that he’s 100% right. Here’s a design scenario to shine some light on abductive reasoning:

What we observe: We observed a lot of people wearing Levi’s branded shirts when we visited five European cities last summer.

What we conclude: Levi’s must be a popular brand.

What we can do with it: Let’s say we are designing for a client who wants to increase public bus ridership. Perhaps we could co-brand busses to feature a Levi’s logo and style, making people think the busses are “cool” and stylish.

Still figuring out the difference between inductive and deductive reasoning? Here’s a helpful video from schmoop:

When we understand different types of reasoning, we can plan our design research to produce the answers we seek.