Relationship between subeo and subeor? or polliceo and polliceor?

Question

The compound word sub+eo seems to appear in two different forms, subeo and subeor. One is a normal indicative form, the other deponent. They appear to mean more or less the same thing. What is the relationship between these two forms? Should they be regarded as completely equivalent synonyms or is there some subtle difference between them?

Is there a evolutionary relationship between the two forms? In other words, is one form more prevalent than the other depending on the time period of use?

There are other words like this, such as polliceo and polliceor where the regular verb and deponent form seem to be exact synonyms.

Answer 1

I would not say the passive forms of subeo are deponent: the ones I saw are rather impersonal passives. An example from Pomponius Mela, De Chorographia I.74.1:

Ubi ad ima perventum est, rursum specus alter aperitur ob alia dicendus. Terret
ingredientes sonitu cymbalorum divinitus et magno fragore crepitantium. Deinde aliquamdiu perspicuus, mox et quo magis subitur obscurior, ducit ausos penitus, alteque quasi cuniculo admittit.

"The farther one went inside, the darker it was."

I could not find any active forms of polliceo in the HP corpus, but Cairnarvon has found a single one (he made a comment below):

It looks like there's exactly one active form of polliceor in the corpus, in Varro (pre-Classical, obviously): ne dares, ne polliceres quid datum est. Nussbaum mentions it along with an instance of a passive meaning in this article (p. 170) discussing polliceor. The significance is up for debate.

In general, there exist various active verbs which have an alternative deponent form that means (roughly) the same thing, such as merero and mereor.

Often times, such forms are used in different periods or by different writers, though perhaps not always. I do not know whether one was usually older or the other.