There's a particular Rule of Evidence in Pennsylvania which is Rule 701. Under Rule 701, a witness who is not testifying as an expert, is limited in testimony in the form of opinions and inferences to those which are based on his perception and helpful to a clear understanding of his testimony or the determination of a fact in issue.
This is called the legal conclusion rule of evidence. It is a rarely used objection, but it is helpful for Chester County DUI lawyers.
For example, when witnesses are asked whether conduct was unlawful or on willful, these terms demand an understanding of the nature and scope of the law which only the trial court may properly conclude. Thus, if a witness concludes that a person conspired or was willful in their actions, that conclusion should only be made by the trier of fact (the Chester County judge). The witness in this case is unfamiliar with the law and may falsely feel that the legal standard is either higher or lower than it really is. Neither event a jury may give too much weight to such a legal conclusion drawn by witness.
A case on point is one in Pennsylvania in 1943 where it was improper for a witness to be asked whether a nurse would disturb a reasonable person. In Commonwealth v. Joseph, this 2004 Superior Court case found that the trial court properly precluded questions to a detective which sought to elicit legal conclusions about emails allegedly used to entrap the defendant. In Commonwealth v. McLean, this 1989 case from the Superior Court found that it was proper to exclude testimony regarding a victim's living arrangements as to whether it was a common-law marriage. Again, in this case, the person testifying did not have the legal expertise to determine what a common law marriage was.
Another case is Commonwealth v. Johnson from 1988 which determined that a psychiatrist was not qualified to testify whether his definition of mental illness was the same as the legal definition of mental illness. Finally, a Superior Court case in 1984 determined that it was correct to 16 objections to questions asking a landlord if you had a duty to see that the tenant operated it's business properly. There are a plethora of federal courts that have found that late meanings can be different than legal meanings. For example, United States v. Lavigne, a 1999 matter, found that there was no error and allowing a prosecutor to ask the defendant if he had forged signatures on checks. The specific reason behind the courts ruling was that forgery was a description of ask that did not come close to a legal conclusion and was more a lay opinion. The court in Lavigne stated, "witnesses can't insist that the prosecutor use euphemisms when inquiring into conduct that the indictment labels a crime. The prosecutor may ask and accused thief whether he stuck up the teller and robbed the bank; he may ask and accuse drug peddler whether he sold drugs to an undercover agent; he may asking accused price fix or whether he joined a cartel; he may asking accused killer whether he murdered the deceased… All are proper subjects of cross examination, provided only that the judge makes it clear to the jury that neither the questioner nor the witness defines the elements of the offense".