The study of the covenanting movement involves differentiating and describing ecclesiastical and political groupings and the individuals who are members of them. While there are always conformists, others are people of strong conviction. It often seems that words are used to describe the intensity of those convictions rather than describe the convictions themselves. For example, writers use radical when they really mean rabid.
The most used labels are radical and conservative. Moderate is also a useful word. Unfortunately, in discussions of Scottish church history, one cannot look back from the 21st century to the 17th without it picking up some connotations from its 19th and 18th century usage on the way through.
Conformists are difficult to describe because they are what they are when they are it: particularly if they can be left alone to be it. They are not conservative in that they do not resist change. They are not radical in that they do not promote it. And, most certainly, the Vicar of Bray has not done their reputation any favours. In the covenanting context, ecclesiastically, conformists are ambivalent on church government and accommodating to a point on worship practices; and politically, they are submissive to the power that is. Their two fears are popery (1638, 1688) and anarchy (1660).
Nevertheless, conformity is not uniformity. Conformity works where minister, patron, and congregation have found a point on the spectrum of unforbidden practice where they are if not comfortable and secure, at least undisturbed.
Radicals want fundamental change. Etymologically speaking, the most radical thing of the 1640s was the petition which asked the English Parliament to abolish prelacy “with all its dependencies, roots and branches”. Having established meaning, word order is important too. Radical Presbyterians want the church to be founded on Presbyterian principles. Presbyterian radicals are those who are Presbyterian in their view of church government and who want fundamental change in politics. For example, David Dickson and Samuel Rutherford were both convinced Presbyterians, but Dickson was more conservative in his politics than was Rutherford. Both were radical Presbyterians; but, of the two, Rutherford was the Presbyterian radical.
It is doubtful that the word moderate was ever used of David Calderwood. Those studying the Scots and the Westminster Assembly consider him a conservative, or even reactionary, Presbyterian. Yet, for most of his life, he was among the most radical Presbyterians. When he questions the accommodation being negotiated at Westminster, he does so because he believes that a fundamental Presbyterian principle is being threatened. He is still a radical Presbyterian. He is not a radical vis-à-vis Episcopacy and a conservative vis-à-vis Independency. That is not how divine right ecclesiology works.
That said, Calderwood is also a conservative. When Scots ministers returned from Ulster in the 1630s, they brought with them some new worship practices which did not please him and which he opposed all the way to the General Assembly.
So, David Calderwood was a Presbyterian. Among Presbyterians, he was a radical Presbyterian. Among radical Presbyterians, he was a conservative. That makes him, without contradiction, a conservative radical Presbyterian: and, in the opinion of Robert Baillie, an immoderate conservative radical Presbyterian.