“Liberal arts” is the higher-ed version of “natural food”: it’s a label anyone can use if they so choose. It has no agreed-upon definitions, or definitions that are so vague that they permit a nearly endless range of claims. Just about any imaginable type of subject or program in higher education can and do claim to be liberal arts, and new institutions or programs have decisively rejected the label (though that may be changing).
So what are you and your colleagues arguing about? If they’re not engineers, they’re basically telling you to get out of their business and tend to your own affairs. If they’re especially rude, they’re telling you they wish you and the other engineers didn’t have a department at your institution. If they are engineers, they’re telling you that they think engineering is special and separate and shouldn’t be subject to the same constraints or requirements as other disciplines and departments.
Presumably you are disagreeing with these views. You want to belong to the wider institution, you see yourself as representing a discipline that is fundamentally similar in its purposes and possibilities to English literature, sociology or philosophy.
What is the similarity that you are gesturing towards by invoking “liberal arts”? Perhaps it is that you think of engineering as a way of thinking about and solving broad, general problems, that it has uncertain or open-ended uses. Perhaps you are embracing the proposition that being part of the liberal arts allows engineering to be combined in unpredictable and creative ways with other disciplines.
You should ask yourself: is any of that a matter of institutional structure, or intellectual disposition? If it’s a set of structural affordances, then what you call engineering might not matter much. It doesn’t help to call engineering liberal arts if an engineering major is sequestered from the rest of the curriculum by forbidding prerequisites and requirements. Or at least that isolation makes it harder to figure out what makes engineering or anything else liberal arts. If belonging to liberal education is a matter of attitude on the part of individual faculty or students, if one can be liberal arts while studying a single discipline within a strongly exclusive environment, well, what exactly is that? Not that such claims would be challenging only when engineers make them: it’s just as hard to pin down what a philosopher, a literary critic, or an economist means when they say “I think in broad and interconnected ways about what I do”. If that’s a polite way of saying, “I am smarter than some group of narrow-minded colleagues”, don’t expect the people being tagged as dumber to appreciate your ambition.
It may help to appreciate where the objection to engineering being labeled liberal arts actually comes from. It may come as much from non-engineers as engineers. It has a history that goes all the way back to the rise of the research university in the 19th Century, and arguably further back than that. To some extent, insisting on including engineering in liberal education has far broader implications. That stance touches on deeply recurrent arguments and anxieties about the practicality and applicability of liberal learning. If it’s worth it to you to make an argument about engineering, you’re going to need to decide not just what your own motivations are for doing so, but also you’ll want to examine the dusty blueprints and obscure reconstructions of liberal learning itself over the past century.