Is v-spec Specific for agent? If so, How to Solve This Problem?

Question

In my syntax classes, I learnt that v-spec is specific for agent role. The thing is, I came across a structure in the resource below:

Radford, A. (2004). Minimalist Syntax: Exploring the Structure of English

He was analyzing the structure of sentence below:

Where is it thought that he will go?

So at first, he gave a structure as below:

And then he said:

Since vP is intransitive (by virtue of the fact that the light verb has no external argument), vP is not a phase, and Transfer cannot apply at this point.

What does that mean? I learned that an agent must always be at v-spec and he is really and agent there. I -at first- thought that go does not have any accusative argument, so he is at V-spec, but that did not make any sense at all. So, from this point, it went through this way below:

My questions are:

1. Is there really any reference that an agent occurs in another place rather than v-spec?
2. If it is possible to see agents in another place, does that apply to all verbs not having an accusative argument but only a PP?
3. If agent is specific to v-spec, then how do we describe the given example above?

Limitations

• Phase Theory must be applied.

Answer 1

Andrew Radford (Radford 2004) discusses it on p. 351.

Go is an unaccusative verb, which means, under Radford's analysis, that the subject originates in spec-VP, unlike in the case of transitive (unergative) verbs, where the subject originates in spec-vP.

This is what Radford proposed. However, it doesn't mean that everyone has the same interpretation of the syntactic behavior of intransitive (unaccusative) verbs.

David Adger (Adger 2003, Core Syntax) argues that the argument of an unaccusative verb (THEME) is always base-generated in comp,VP - so, at least his analysis is better in this regard because it doesn't violate UTAH. The argument then moves to spec,TP (to satisfy EPP on T).