How are we to develop the Illative sense? First of all there is the small question as to whether there exists such a thing as the illative sense as Newman understood it? His account of it persuades me but it may be something that you need to have some experience of to accept, the point being that the overleaping of intermediate steps towards a truth is not likely to be supported by methods which depend on them. It’s the lifting yourself up by the seat of your own pants without external aid aspect that gets people worried. Here surely is well dug, manured and with tilth like fine breadcrumbs, soil, ready for the seeds of self delusion. That is a sensible point and it can only be answered by an admission and an admonition - caveat rhetor. The man who has served his apprenticeship to the truth using all the standard tools for its attainment is one to whom the truth may be revealed by illative means. He has by long attention achieved a connaturality with the truth. It speaks to him.
Elisa Freschi’s points in the comments are well taken.
T. Arnold Haultain’s strictures (pub. 1885) on the illative sense are to be found at the Internet Archive: