The phrase "a true reason for" is correct and usable in written English.
It can be used when discussing the validity or authenticity of a reason behind an action or decision.
Example: "The committee needed to find a true reason for the sudden change in policy to address the concerns of the stakeholders."
Alternatives: "an actual justification for" or "a genuine explanation for".
We do not tell our neighbor that our government has declared war without a true reason, but only for an abstract political theory about how to control the Middle East.
"Hypotheses are… sometimes very necessary… in all cases when we cannot discover the true reason for a phenomenon and the attendant circumstances, neither a priori, by means of truths [identified as principles in §53] that we already know, nor a posteriori, with the help of experiments" (IP §60).
This sense of authentic purpose, the true reason for a company's or product's existence in the world, can be powerful and compelling.
The report would have attributed the lane closures to a traffic study, covering up the true reason for the closures: political retribution against the mayor of Fort Lee for failing to endorse Christie's 2013 re-election, Wildstein testified.
The documentary claims that the U.S. Centers for Disease Control and Prevention concocted a conspiracy to cover up the "true" reason for America's rising autism diagnosis rates: vaccines.
The event was billed as an honorary graduation ceremony, and the true reason for the trip to Downing Street only became clear at the last minute.
Nobody outside China's closeted leadership knows the true reason for the maneuvers, beyond a general and intangible sense of uneasiness over the degree to which freer speech is taking root here.
Stephen Cantor, solicitor for the Derbyshire Families Association, said: "Everyone is hopeful there will be a proper outcome to the investigation and that the true reason for the loss of the Derbyshire comes out.
In a series of laboratory experiments, we reveal that the true reason for coordination failure is strategic uncertainty, which can be reduced almost completely by introducing an appropriately designed mechanism of (inter-group) competition.
Regardless of the true reason for the experienced "side effect", a patient's perception of the reason for the side effect may be more important in predicting adherence.
