Apparent exceptions are concerning, considering, pending, generally speaking, etc. The first three may be classed as prepositions ([§ 355]), the last as an independent participle.

We fought every day, and, generally speaking, twice every day.—De Quincey.

Note. The rule in [§ 339] does not apply to such phrases as on entering, after investigating, etc., in which the words in -ing are not participles, but verbal nouns ([§ 348]). Thus the following sentences are grammatical:—“On entering the room, a strange sight appeared”; “After investigating the subject, the plan was adopted.” Such expressions, however, should be used with caution, since they are sometimes awkward or ambiguous.

340. A participle may be modified by an adverb, an adverbial phrase, or an adverbial clause.

341. A participle may take an object if its meaning allows.

The participle, with its modifiers and such other words as are attached to it, is sometimes called a participial phrase.

342. A participle may be used as a pure adjective.