First, no one can tell you what is "generally taught" in the thousands of law schools across hundreds of jurisdictions.
Second, dishonesty is defined by the OED as "deceitfulness shown in someone's character or behaviour" and deceit is defined as "the action or practice of deceiving someone by concealing or misrepresenting the truth".
"Someone" can be the person who makes the statement so if you deceive yourself or someone else you are being dishonest. You do not have to make a statement to be dishonest; not saying something can be deceitful.
However, dishonesty is not in and of itself a crime or a tort; it only becomes so when the law imposes a duty to be honest. When that happens, the statute (if applicable) and the case law is usually pretty clear about what honesty requires. This will differ between jurisdictions and within jurisdictions with context.
For example, many jurisdictions impose an obligations on business not to engage in "false or misleading" conduct. However, you can tell lies and still comply with the law because obviously outrageous advertising claims (e.g. "Sale of the Century", "The greatest thing since sliced bread") while (probably) false are not misleading.
Alternatively, you can be scrupulous about not telling lies and still be dishonest. A case in NSW (name escapes me) where a potential buyer of a restaurant asked "How many does it seat?" and receiving a reply of "X", a perfectly accurate answer based on the number of place settings, was able to successfully sue when he discovered after the purchase that it was licenced to seat "Y"; substantially less than "X". The judge held that while the statement was a factually accurate response to the literal question posed, it was dishonest in the context of the transaction the parties were contemplating.