Demand capture converts buyers who are already looking for a solution, for example through Search ads on category keywords. Demand generation creates awareness and interest before that search happens, for example through LinkedIn and content. You cannot capture demand that does not exist yet.
Two different jobs
Demand capture is harvesting: the intent already exists and you compete to be chosen. Demand generation is planting: you build awareness in buyers who are not searching yet. Most underperforming B2B accounts are pouring budget into capture for a category that is too small to capture from.
Getting the sequence right
If few people search for what you sell, Search keywords sit flagged "low search volume" and your ads never serve. In that case you generate demand first, often with outbound and LinkedIn, then layer in Search once the searches exist. We walk through a real example in Search ads don't create demand, they tax it.