One feature of Tax Court litigation surprises almost every taxpayer who encounters it for the first time: the burden of proof is largely on you, not on the CRA. The Minister's conclusions are presumed correct until the taxpayer proves otherwise. Understanding how that onus works — and how documentary and oral evidence combine to discharge it — is the single most important thing to grasp about how tax appeals are decided. This guide explains the taxpayer's onus, the role of the Minister's assumptions of fact, what it means to "demolish" them, the difference between documentary and viva voce evidence, and why credibility so often decides the outcome.
The taxpayer's onus
Canadian tax assessments are presumed valid. When the Minister reassesses, the law treats the assessment as correct, and it falls to the taxpayer — the appellant — to show that it is wrong. This is different from the criminal model, where the state must prove its case; in a civil tax appeal the taxpayer must prove, on a balance of probabilities, that the reassessment does not hold up. There are exceptions — most notably gross-negligence penalties under subsection 163(2), where the burden shifts to the Crown to justify the penalty — but as a general rule the appellant carries the onus on the substantive reassessment.
The Minister's assumptions of fact
The mechanism through which the onus operates is the set of assumptions of fact the Minister pleads in the reply. When the CRA reassesses, it relies on factual conclusions — that a deposit was income, that an expense was personal, that a transaction lacked commercial substance. In the litigation, the Crown sets those assumptions out in its reply, and they are taken as presumed true unless the taxpayer rebuts them. This is why the reply is the most important document the Crown files: it is, in effect, a map of everything the taxpayer has to disprove. You cannot rebut an assumption you have not identified, so the first task in any appeal is to read the assumptions one by one and build evidence against each.
"Demolishing" the assumptions
The standard the taxpayer has to meet is often described as demolishing the Minister's assumptions. The taxpayer makes out a prima facie case — credible evidence that, if accepted, displaces an assumption — and the evidentiary burden then shifts to the Crown to prove the assumption on the balance of probabilities. A prima facie case is one supported by evidence that raises a degree of probability the assumption is wrong; it does not require certainty. Once the taxpayer demolishes an assumption with credible evidence, and the Crown has nothing to put against it, the assumption falls and the reassessment built on it cannot stand. Much of trial preparation is figuring out, assumption by assumption, what evidence will demolish each one.
The case is heard de novo
The Tax Court hears the matter de novo — fresh, on the evidence before the Court — not as a review of what the auditor or the Appeals officer decided. This has a liberating consequence. During an audit, the CRA may disregard evidence it considers imperfect; the Tax Court applies the law of evidence and weighs what is actually presented. A documentary gap that doomed a position at the audit stage can sometimes be overcome at trial through sworn testimony and corroborating records. The forum changes what counts as proof.
Documentary evidence
Most tax disputes turn on facts, most facts turn on documents, and the document record is the backbone of an appeal. Bank statements, invoices, contracts, ledgers, corporate records, valuations, and correspondence are the raw material from which a case is built. Documentary evidence has the great advantage of being contemporaneous and difficult to dispute. Organized, labelled documents that a witness can explain are persuasive; an unsorted mass of paper is not. Where original receipts are missing, secondary records — credit-card statements, bank records, third-party confirmations — can still carry real weight before a judge, even where an auditor refused to accept them.
Viva voce evidence
Viva voce evidence is oral testimony — live evidence given by a witness under oath, in the witness box, subject to cross-examination. It fills the gaps the documents leave: what a transaction was for, why a decision was made, what the parties intended, what happened where no record was kept. A judge can accept sworn testimony as direct evidence of what occurred. Where the Crown has no real evidence to contradict credible oral testimony, an assumption resting on suspicion or inference may not survive. Documentary and viva voce evidence work together — the documents anchor the testimony, and the testimony explains the documents.
Why credibility decides cases
Because so much of a tax appeal comes down to oral testimony explaining a documentary record, credibility is frequently decisive. A witness who has reviewed the records, knows the chronology, answers candidly, admits the limits of their memory, and withstands cross-examination strengthens the case. A witness who guesses at dates and figures, contradicts the documents, or appears evasive can undermine an otherwise strong position. Credibility is not about polish; it is about consistency, candour, and command of the facts. This is why witness preparation — genuine familiarity with the file rather than rehearsed answers — is so central to a successful appeal.
Expert evidence
Some appeals require an expert report — a business valuation, an accounting reconstruction, a transfer-pricing analysis. Expert evidence is admitted under the Court's rules: the witness must be qualified, the report served in advance, and the expert witness is subject to cross-examination. On technical questions a judge is not otherwise equipped to resolve, a well-prepared expert opinion can be the difference between an assumption that survives and one that falls.
Putting it together
A well-built appeal works backward from the assumptions: identify each assumption of fact in the reply, decide what evidence demolishes it, assemble the documents, prepare the witnesses who can speak to them, and obtain expert evidence where a technical issue demands it. The whole exercise is about meeting the onus the law places on the taxpayer with evidence credible enough to displace the presumption of correctness. How that evidence is presented on the day is described in What to Expect at a Tax Court Hearing.
How we help
Barrett Tax Law builds Tax Court appeals around the assumptions of fact the Crown pleads — organizing the documentary record, preparing witnesses to give credible viva voce evidence, and engaging expert witnesses where a valuation or accounting question requires it. You can read more on our Tax Court of Canada page, and on the litigation overall in The Tax Court of Canada Appeal Process.