HIs first essay was "On Liberty and Necessity," a topic much discussed since Thomas Hobbes' famous essay of the same title.

This essay is cited as the first to use the term "Libertarian." For Belsham it was a term of abuse. Liberty was nearly synonymous with libertine, a description of a person with no responsibility.

Belsham dismisses the ideas of the Libertarians, citing the foreknowledge of God, as did Hobbes and the religious leaders Luther and Calvin before him.

Belsham is a Necessarian, as he describes his fellow determinists.

Here he describes the confusion in the libertarian's view of a "self-determining power."

By the self-determining power therefore must be meant, if indeed it has any meaning, either the actual exertion of volition, or the mental energy which precedes volition, and which is the efficient cause of it. If it means the actual exertion of volition, then the assertors of this power evidently confound the cause with the effect, making the act of volition prior to itself, distinct from itself, and the cause of itself. But if it means the mental energy preceding and producing volition, it is then plainly equivalent to the term motive, and the question is reduced to a mere verbal controversy; for this mental energy, denoting only a particular disposition and state of mind, muff itself have resulted from a previous disposition of mind, as likewise that previous disposition from one yet more remote: — a regular and uninterrupted concatenation of volitions thus extending itself backwards to the original source of agency, each volition or mental state, like wave impelling wave, arising from preceding, and giving rise to succeeding states or definite situations of mind analogous to itself, and corresponding to those immutable laws by which the mental no less than the material world is governed by infinite wisdom and power.

But the term motive, according to the Necessarian definition, includes all those previous circumstances which contribute to produce a definite volition or determination of the will. To what purpose then attempt to distinguish between the power and the motive of determination, when the ideas precisely coincide; the definite cause of a definite volition being all which is really meant by either?

Or where is the difference between the Libertarian, who says that the mind chooses the motive; and the Necessarian, who asserts that the motive determines the mind; if the volition be the necessary result of all the previous circumstances?

The distinction in this case can only amount to an idle and trifling evasion; and it is evident, that in order to preserve a shadow of liberty, its advocates make no scruple to adopt a gross impropriety of expression: to boast, that the mind chooses the motive when the mind is restricted to a definite choice, is ridiculous; and it is in fact as great a solecism, as to affirm that the volition chooses the motive: for the choice of the mind is not prior, but subsequent to the motive; it is therefore not the cause, but the effect of the motive; and this pretended mental choice manifestly neither more nor less than the necessary determination of volition.

(On Liberty and Necessity, Essays (1789), pp.10-12)