Explainer: Bloom's Taxonomy

I was asked once: what makes Higher Education ‘higher’? The question has really stuck with me! I’ve heard lots of answers, some of them conflicting, but none of them unreasonable. The most common responses seem to appeal to something about the quality or type of the thinking that happens in degrees.

Getting students to memorise times tables isn’t the kind of thinking Universities are excited about. To recall facts is an important activity, but the category of ‘recalling’ is not the kind of thinking which seems to match our sense of what we’re training students to do. To ‘analyse’ something seems closer: there is something about the focus on how a phenomenon works or how to interpret complex data which resonates more strongly with what we think a degree should help people to do.

Bloom’s Taxonomy is one way that these intuitions have been formalised, and is normally presented as an attempt to articulate the types of thinking which can be seen as ‘higher’ and ‘lower’-order. Often shown as a pyramid, it conveys an implicit sense of hierarchy: the ‘good stuff’ is at the top.

A representation of Bloom’s Taxonomy, with an ascending series of cognitive skills: knowledge, comprehension, application, analysis, synthesis, evaluation. (Credit: Corydave)

Theoretical Basis of the Taxonomy

I think the hierarchy really resonates with a lot of educators, but so far as I can tell there is no cognitive rationale for the ordering of different categories of thought in this hierarchical way. It’s probably best seen as an expression of a philosophy of design: it describes the goals of a certain type of education.

The values coded into a hierarchical representation are therefore political and contestable. Several widely-used versions of the taxonomy now exist, and they seem to be adapted fairly freely by people to suit their needs. 

Use of the Taxonomy

In my experience the value of Bloom’s Taxonomy lies in its ability to clarify. You might not agree with the taxonomy, but I think the menu of ideas it presents can still be really helpful in trying to articulate your own ideas. This can be through rejecting the taxonomy; we often clarify our own views by disagreeing with things.

Intended Learning Outcomes

Academics are deeply immersed in the structures of knowledge within a discipline, and the challenge of Bloom’s Taxonomy is to operationalise disciplinary understanding into specific actions. I might be excited for my students to develop a deep grasp of the selection rules appropriate to molecular UV-Vis spectroscopy, but what does that mean they should be able to do?

The gift of a conversation between the disciplinary knowledge and the generic taxonomy is a greater clarity about what you’re trying to accomplish. This clarity is - in my experience - the hallmark of every scandalously-effective educator I’ve ever met. I’m sure there are other ways to develop this clarity, but this is one of them.

Biggs’ SOLO taxonomy might be seen as a parallel attempt to develop a hierarchy of cognitive learning outcomes.

Assessment

One way to use the taxonomy is in the choice of verb in exam questions. For example, an exam question might be written in several different ways depending on how high an order of thinking you want to demand of students.

NAME a square planar anticancer agent. (Know)

EXPLAIN why cisplatin and transplatin have very different cytotoxicities. (Understand)

The structures of cisplatin and satraplatin are shown below, together with their IC50 values in several cell lines. By appeal to the mechanisms of action, COMPARE the activities of these two molecules. (Analyse)

These are three very different questions! But the taxonomy can prompt (even inspire) you to navigate familiar material in new ways. I think this is often really useful. The first year you teach a course it’s easy to dream up exam questions, but the fifth?

It also helps to communicate the task more clearly to students. Very specifically, it steers you away from the verb “discuss”. “Discuss” is a verb which can mean very different things; if you can possibly pick a more specific rubric instruction then you’ll help your students to do what you really want them to do.

(The University of Miami has produced a list of verbs associated with each level of the taxonomy. You will notice that some verbs appear in several categories.)

Teaching

Disciplinary educators often struggle to distinguish between knowledge and skills when they have mastered both. Bloom’s Taxonomy helps to tease these apart systematically. It often isn’t enough to teach students the content if your ambition is to have them demonstrate skills. 

So Bloom’s Taxonomy helps constructively-aligned teaching because it clarifies something about the skills. If you want students to analyse data about the rates of substitution for aqueous metal cations, you might consider modelling an analysis or two in your lectures (“so to explain this table of substitution rates, the key principles are charge, size, and electron configuration. Let’s look first at Ca(II), Mn(II) and Zn(II).”).

Criticisms

It’s worth weighing up a few of the criticisms of the taxonomy in a blog, because they rarely get a hearing in other spaces. Many people are exposed to the taxonomy in ways which rush them through to the point of applying it to their teaching.

Why is ‘Understanding’ so low/absent?

Comprehension - the second level of the taxonomy - is arguably synonymous with ‘understanding’. But most educators I’ve met see understanding as something of a much higher order. The ‘penny-drop’ moment when a student ‘gets’ something is something in which we find great value, for example. Surely that should be higher up?

Defenders of the taxonomy would argue that the lower-order skills aren’t less valuable, but simply underpin the higher-order ones: to apply knowledge, you must recall it. The foundation of a house isn’t less important than the roof. Bloom’s challenge to disciplinary educators is often about how ‘understanding’ is expressed. How do you test whether someone has ‘understood’ a concept like the inert pair effect? I think this challenge is often useful.

Problem Solving

In the last few decades, Chemistry has increasingly been framed as a discipline which values “Problem Solving” as a skill graduates should have. This term does not appear on the taxonomy. Is the taxonomy just useless for problem solving disciplines?

Articulating which skills are required to solve a problem is often hard to do, but I worry that most exam “problems” are really recall questions. Sincere problem solving normally involves the application of knowledge in some way to satisfy some puzzle, which might involve relatively high-order thinking. It might be that there are useful parallels between the taxonomy and Problem Solving, but they are undoubtedly a little strained.

At the same time, Chemistry is more-or-less uninterested in Critical Thinking – which most other disciplines see as the whole point of Higher Education. It’s interesting to consider whether an over-commitment to Problem Solving might bar chemists from accessing cognitive skills which other disciplines see as highest-order. Why don’t we get in on this Critical Thinking racket?

It’s also worth considering how Problems are arguably premised on a weak basis in the lower-order skills. For example, an exam question might ask someone to calculate the irreps spanned by the C=O stretching modes of fac-[Mo(PPh3)3(CO)3]. What if I just know that they span a1+e? Is it a Problem any more? Did I solve it by recalling the answer?

The Skills Agenda

If the purpose of Higher Education is about higher-order skills, there is a way of viewing education as being about maximising exposure to those skills. One way to do this might be to withdraw focus from the lower-order skills.

I think this is the area where the taxonomy sits in the greatest tension with the disciplines, because the content of a discipline is more demonstrably baked into lower-order cognitive skills than higher-order ones. The obviously-unique thing about a subject is the facts it has.

But what this discussion opens up is the chance to see the wider tension between a skills-based view of the curriculum and a content-based one. Generic skills don’t ever exist without a highly-specific context. You can’t think without thinking about something! Lower-order skills enable higher-order ones. You can’t find really ‘get’ what’s going on in borazine without knowing a lot about benzene.

What composition of higher- and lower-order skills is appropriate? It might be that there are good reasons to consider what the consequence of the push towards skills has been. I think I’m broadly in favour of minimising trivial memorisation tasks (memorising the periodic table), but at the same time it seems valuable to have ready access to a rich range of examples when learning chemistry.

Conclusion

Bloom’s Taxonomy is a popular model with some important merits. It helps educators to systematically consider generic cognitive skills when navigating the structures of knowledge specific to their disciplines. This can substantially enrich the way we construct outcomes, assessment, and teaching.

At the same time, there are important weaknesses. The philosophy of a skills-driven education might sit poorly with some educators at times, and the ‘fit’ of the disciplinary structures with the taxonomy can sometimes be poor. It also makes no claim to describe non-cognitive aspects of education (e.g. the affective domain), and treating it as a totalising description of education is not appropriate.

So I think it’s worth treating as one coherent way of reflecting on education – as one perspective on what we’re doing. If it isn’t taken too seriously and isn’t completely written off, I think it can really add something to how we think about education.