The following summary is taking from Shepherd's Essay on Cause and Effect, pp. 186-187. The "inquiries of this nature" she is considering at this juncture of the work are accounts of the cause of life, and is arguing that a causal account like her own is needed for success in scientific discussions like this.

But as long as the notions of Mr. Hume shall prevail, inquiries of this nature will be instituted in vain; nor indeed is there any received doctrine upon the relation of Cause and Effect, which can be securely used, as an efficient instrument in the advancement of science.

Bishop Berkeley thought a Cause must necessary by active, and so a spirit! And it is universally imagined that a Cause is, in its very essence, before its Effects.

There is also, a notion that one object is sufficient to an event; when many are perhaps wanted in order to produce it.

I pretend not to have found the whole nature of this relation;-But I shortly recapitulate what I have advanced.

1st.--The junction of two or more qualities or objects is wanted to every new creation of a new quality.

2dly.--That any one of the qualities or objects needful in order to the formation of another, may be termed a Cause, because absolutely necessary, and, when all the other needful circumstances are duly placed with which it is to unite, efficient to its production.

But, 3dly. The whole number of objects existing, which are necessary to it, may also, under one complex idea, be deemed the one whole cause necessary.

4thly.--The union of these, is the proximate Cause of, and is one with the Effect.

5thly.--The objects therefore are before the Effects, but the union of them is in and with the Effects.

This ambiguity, arising from the necessity of naming each object, wanted to an end, and all that are wanted to it, and the junction necessary to it, the Cause of it, is a fruitful source of error in every branch of analytical philosophy.

6thly.--When Effects or new qualities are once formed, theymay re-act as Causes, in order to keep up the original objects, which contributed to their formation.

7thly.--Although the very word Effect implies a change in qualities, yet among a set of new qualities formed, all of them are not therefore entirely changed.

The spark first elicited from the tinder, is kept separate,as to its appearance, its warmth and light, amidst all the alteration, in which it involves the objects it approaches.

8thly.--It is not necessary, however, that any of the Effects, should resemble any of the objects, by whose union they are caused;-and in general, an entire mixture, junction and consusison of qualities involves the whole original objects in ruins, whilst it strikes out a vast many new and altered ones, creating other masses, other complex objects, totally unlike those whose union was their Cause. On the other hand, it sometimes appears that nature intends to render one individual essence, the prime object intendeed to be preserved; and therefore in its mixture with others, ordains that they shall only administer to it, by contributing to the perpeutal nourishment, support, and increase of its qualities; as in the growth of plants and animals; or the vigour, improvement, character, individuality, &c. of the sentient principle.--

Lady Mary Shepherd, An Essay upon the Relation of Cause and Effect. T. Hookham (London: 1824) 192-194.