OftenBen I do not believe that if you do not disclose you are dating other people in the first several casual dates that you are lying serially or by omission. There are lots of things you may choose not to disclose in the first few dates and, as a date-e and dater, this should be understandable. There is a lot of past trauma, as well as past happiness, that may end up being relevant to someone you date that you probably should disclose at some point - that doesn't mean you have to, or even should, right away. If you unpack all your baggage, "full disclosure" style, on a first date, you're not going to get a second one.

For instance, (fictional example), if I had attempted suicide in my past, that is something I feel a romantic partner should know. That is not something I think anyone should feel they have to disclose in the first, say, 3-5 dates however.

You should try to figure out if you like a person and trust them, before diving into disclosures. I think honestly that includes "I'm dating other people."

On the other hand, you should also always assume if you haven't had a conversation about monogamy, that your date could be and probably is dating other people. Especially, again, in the first 3-5 dates where you're honestly just trying each other on for size.

However, I'm not saying this is a bad approach - I'm just saying i don't believe not disclosing it woud constitute a lie unless/until the dating began to take a more serious flavor to it.