What do you mean by "ad hoc"?
"Ad hoc" is Latin for "for this [purpose]" and it's used to describe modifications or additions to a proposed explanation, for which the only "evidence" or support offered for that addition is the failure of explanation to hold up without it.
For instance, I might explain gravity with an explanation about angels pushing down on people's shoulders, and when you ask "well, if that's true, how come we can't see the angels?" My response "because they're invisible" is an ad-hoc explanation because the only evidence that these angels
are invisible is the fact that otherwise, my theory about angels can't explain why you can't see them.