I was wondering if there is a difference in the usage between merkwürdig and seltsam. My German to English dictionary translates both to peculiar or odd. Can I use them interchangably?
Colloquially, they are usually interchangeable. In any case, you should consider the differences.
Since merkwürdig derives from merken (remember) and würdig (worthy), it characterizes something deserving to be remembered, or at least to be noticed (bemerken). There’s a synonym called bemerkenswert which still conveys the original meaning.
On the other hand, seltsam means that something’s seldom (selten) and that it’s odd and unusual. Today, it’s used like “odd” in English (like in “That’s odd” or “the child exhibits an odd behavior”).
If you look up their etymologies, you’ll realize that they originally had a very distinct meaning. In everyday use, you usually don’t have to ponder the differences.
Based on the literal meanings, I would think merkwürdig is closer to the English term curious (
That's a curious way to make a cake) when applied to a phenomenon while seltsam is more like unusual or awkward. At the same time, common meaning has probably left the logic, as often happens in language.