If you are applying to a City law firm, there is a good chance you will sit the Watson Glaser test before anyone reads your cover letter. It is the most widely used critical thinking test in legal recruitment, and for many firms it is an early, hard filter. The encouraging part is that it rewards preparation more than almost anything else in the process, because most of what it catches is people who do not yet know what each question is really asking.
The Watson Glaser Critical Thinking Appraisal measures how well you reason with evidence: whether you can separate what a passage proves from what it merely suggests, spot hidden assumptions, and judge the strength of an argument. Firms use it because that is exactly the skill a trainee solicitor needs, and because it is very hard to fake.
Which firms use the Watson Glaser
The test is closely associated with law. Many of the largest commercial firms use it or a test in the same critical-thinking style at the application or assessment-centre stage. It is common across the Magic Circle and other City and US firms in London, and it also appears in some graduate schemes outside law.
The exact number of questions and the time limit vary by version and employer. A common format is around 40 questions in roughly 30 minutes, though some firms run untimed or differently timed versions. What does not change is the five-section structure, so that is what you should practise.
The five sections, explained
Every Watson Glaser is built from the same five subtests. Each rewards a slightly different discipline, and each has a trap that catches people who read too quickly.
1. Inference
You read a short passage of facts, then judge whether each proposed inference is True, Probably True, Insufficient Data, Probably False, or False, based only on the passage. The whole game is proportion and certainty. If a passage says nine in ten students passed, then "a randomly chosen student passed" is probably true, not true. If the passage says nothing about a point, the answer is insufficient data, however reasonable your real-world guess would be.
Passage: "Of 200 applicants, 150 named a specific deal the firm had worked on." Inference: "Most applicants named a specific deal."
True. 150 of 200 is three quarters, which is most. The passage states it directly, so this is proven, not merely likely.
2. Recognition of Assumptions
You are given a statement, then asked whether a proposed assumption is made or not made. An assumption is something taken for granted for the statement to hold. The trap is to accept anything that sounds plausible. Only mark "assumption made" if the statement genuinely depends on it.
Statement: "Send a thank-you email after an interview, because interviewers remember candidates who do." Assumption: "Being remembered benefits the candidate."
Assumption made. Being remembered is only a reason to send the email if it works in your favour, so the statement takes that for granted.
3. Deduction
You judge whether a conclusion follows or does not follow from the premises, using only the premises and treating them as true. This is formal logic, not real-world knowledge. Watch for converse errors: "all partners attend the meeting" does not mean "everyone at the meeting is a partner".
Premises: "All partners attend the Monday meeting. Leah does not attend." Conclusion: "Leah is not a partner."
Follows. If she were a partner she would attend, and she does not, so she cannot be one. That is a valid contrapositive.
4. Interpretation
Similar to deduction, but the bar is "beyond reasonable doubt" rather than strict logic. You read a passage, then decide whether a conclusion follows or does not follow. A correlation in the data does not let you conclude cause, and one year's figures do not prove next year's.
5. Evaluation of Arguments
You judge whether an argument is strong or weak in response to a question. A strong argument is both directly relevant and important; a weak one is trivial, off-topic, or an appeal to habit. "We have always done it this way" is weak. A concrete consequence that bears on the decision is strong.
The thread running through all five: answer from the text, not from what you know or assume. Almost every wrong answer comes from importing outside knowledge or from treating "likely" as "certain".
How it is scored, and the pass mark
Most firms do not publish an exact pass mark, and it can move with the applicant pool in a given year. As a working guide, a score around the 75th to 80th percentile is competitive for commercial law, and stronger firms sit higher. What matters in practice is being comfortably above the firm's cut-off, and the way to get there is format familiarity: knowing, before you read the options, exactly what each section is asking you to judge.
There is usually no negative marking, so never leave a question blank. If you are running out of time, answer everything.
How to prepare, the honest version
- Learn the five verdicts cold. Most marks are lost by confusing "probably true" with "true", or "insufficient data" with "false". Drill the distinctions until they are automatic.
- Answer only from the passage. Physically resist adding your own knowledge. This single habit fixes most inference and interpretation errors.
- Practise under time. The pressure is real. Around 45 seconds a question is typical, so you need the reasoning to be fast, not laboured.
- Review every explanation. Getting a question right for the wrong reason will not survive a harder version. Understand why the answer is what it is.
- Do full timed mocks near the date. Stamina and pacing are part of the test.
Common mistakes
- Importing outside knowledge into inference and interpretation questions
- Treating a likely conclusion as a certain one, and vice versa
- Making converse errors in deduction ("all A are B" read as "all B are A")
- Marking an argument strong because it is true, rather than because it is relevant and important to the question
- Leaving questions blank when there is no negative marking
- Practising without timing, then freezing on pace on the day
Once the five sections and their traps are second nature, the Watson Glaser stops being a gatekeeper and becomes a stage you clear. The fastest route there is reps in the real format, which is exactly what the free practice below is for.