Castle Howard mottoes

[Bert]

Castle Howard is associated with two mottoes: "Volo non valeo" and "Credo ergo facio". The first means, I think, "I wish - I am not strong", and the second means "I believe, therefore I do". The second is fairly straightforward, but what does the first mean? If it means "the spirit is willing, but the flesh is weak", it is a very strange motto, since they are usually of a much more positive nature.
Does anyone know why there are two mottoes? Perhaps they are from different sides of the family?

[gen2]

There are a few hundred hits on google suggesting that Volo, non valeo means I am willing but unable