Albert Barnes Commentary Acts 21:29

"For they had before seen with him in the city Trophimus the Ephesian, whom they supposed that Paul had brought into the temple." — Acts 21:29 (ASV)

In the city. In Jerusalem. As he was with Paul, it was inferred that he would accompany him everywhere.

Trophimus. He had accompanied Paul on his way from Ephesus (Acts 20:4).

Whom they supposed, etc. This is a very striking illustration of the manner in which accusations are often brought against others. They had seen him with Paul in the city; they inferred, therefore, that he had been with him in the temple. They did not even pretend that they had seen him in the temple; but the inference was enough to inflame the angry and excitable passions of the multitude.

So it is with the accusations that people now often make against others. They see one thing; they infer another. They could testify to one thing, but they conclude that another thing is also true, and that other thing they charge against them as the truth. If people would state facts as they are, no small part of the slanderous accusations against others would cease.

An end would be put to most charges of falsehood, error, heresy, dishonesty, double-dealing, and immorality. If a statement is made, it should describe the thing as it was. If we attempt to state what a person has done, it should not be what we suppose that person has done. If we attempt to state what a person believes, it should not be what we suppose that person believes.