What is professional skepticism?
ISA 200.A20 treats professional skepticism as a precondition for applying every other ISA. It runs through risk assessment and evidence evaluation, from planning through to the opinion. In practice, it means you do not accept audit evidence at face value and you do not resolve doubt in management's favour without corroboration.
The standard draws a direct link between skepticism and fraud. ISA 200.A21 acknowledges that the auditor may accept records and documents as genuine, but that acceptance does not relieve the auditor of the obligation to consider their reliability. Most files break down at exactly this point. The engagement team accepts a management explanation that sounds reasonable and documents it without further testing. What the file does not show is what the team did to test whether the explanation was true.
ISA 240.12 reinforces this by requiring the engagement team to set aside prior-year trust when considering fraud risk. A client's track record is relevant context. It is not a substitute for current-year evidence.
Key Points
- Skepticism is an attitude that applies to every stage of the audit, not a procedure you perform once.
- Inspectors flag insufficient skepticism more often than almost any other single finding category.
- Accepting management explanations without corroboration is the most common failure point.
- Your file must show how you challenged assertions, not just that you received them.
Why it matters in practice
The FRC's 2023 annual inspection report flagged insufficient professional skepticism as a recurring finding, particularly around revenue recognition and management estimates. Files accepted management representations on significant judgments without testing the underlying assumptions against external data.
ISA 200.A22 requires the auditor to consider the reliability of documents the entity provides. Teams often document that they "obtained and reviewed" a schedule without recording what they did to verify it. Obtaining is not testing. The file must show both the procedure performed and the conclusion reached on reliability.
Worked example: Van Houten Machinebouw B.V.
Client: Dutch precision engineering firm, FY2024, revenue €38M, Dutch GAAP (RJ) reporter.
During fieldwork, the engagement team identifies a €1.2M year-on-year increase in capitalised development costs. Management explains that the increase reflects a new product line entering the development phase, with technical feasibility demonstrated by internal test results.
Challenge the representation: The team requests the internal test reports, board minutes approving the project, the feasibility assessment prepared under RJ 210, and the external consultant's validation letter.
Test the explanation independently: The team compares the capitalised amount against the approved project budget and checks whether the €1.2M increase is consistent with the project timeline. Management claimed technical feasibility was achieved in Q2. The team verifies this against the engineer's sign-off date and checks whether any costs capitalised before that date should have been expensed under RJ 210.406.
Evaluate and conclude: The external consultant's letter confirms feasibility was established in Q2. The budget approval covers the full €1.2M. But costs capitalised before the Q2 date total €180K. The team challenges management on whether those pre-feasibility costs meet the recognition criteria under RJ 210. Management reclassifies €180K to the income statement.
The file shows that the team tested a plausible management explanation against independent evidence and obtained a €180K adjustment as a result. The skepticism is visible in the working paper, not assumed.
Professional skepticism vs professional judgment
Professional skepticism and professional judgment are distinct but linked. ISA 200.13(l) defines skepticism as the attitude. ISA 200.13(k) defines judgment as the application of relevant training and experience in making informed decisions. Skepticism tells you to question the evidence. Judgment tells you what to do with the answer.
On an engagement, the practical difference shows up at documentation. A reviewer can see judgment in your decisions (which benchmark you selected, which testing approach you applied). Skepticism is harder to see. It appears in the file as the question you asked before making that decision and the corroboration you sought before accepting it. If the file shows the decision but not the challenge that preceded it, the judgment is documented but the skepticism is not.
Key standard references
- ISA 200.13(l): Defines professional skepticism as a questioning mind, including a critical assessment of audit evidence.
- ISA 200.A20–A24: Application guidance on maintaining skepticism throughout the engagement.
- ISA 240.12: Requires the team to set aside prior-year trust when assessing fraud risk.
- ISA 200.A22: Requires the auditor to consider the reliability of documents and responses to inquiries.
Related terms
Related reading
Frequently asked questions
Is professional skepticism the same as distrust?
No. ISA 200.A20 treats skepticism as a precondition for applying every ISA — it means questioning evidence and seeking corroboration, not assuming management is dishonest. It sits between blind trust and suspicion.
How do inspectors assess whether skepticism was applied?
Reviewers look for visible challenge in the working papers: what questions the team asked, what corroboration was sought, and whether management explanations were tested against independent evidence rather than accepted at face value.