Why didn't Gandalf take Frodo with him to Isengard?

Question

In The Fellowship of the Ring, why didn’t Gandalf take Frodo (and the Ring of Power) with him to Isengard?

Since Gandalf was unaware that Saruman had joined forces with Sauron, why wouldn’t he want to keep Frodo and the Ring close by at all times?

Answer 1

Canon (the books)

Gandalf is keen that Frodo avoid drawing attention to himself:

If I just vanish like Bilbo, the tale will be all over the Shire in no time.'

'Of course you mustn't vanish!' said Gandalf. 'That wouldn’t do at all! I said soon, not instantly. If you can think of any way of slipping out of the Shire without its being generally known, it will be worth a little delay. But you must not delay too long.'

^{Fellowship of the Ring Book I Chapter 3: "Three is Company"}

Although he doesn't say this outright, Gandalf is unquestionably trying to throw the Ringwraiths off Frodo's trail; if nobody even knows that Frodo has gone, let alone where he's gone, then that may buy Frodo some time to get to relative safety.

On the other hand, if every hobbit in the Shire sees Frodo riding out from Bag End on the back of Gandalf's horse, it would rather give the game away. In a less extreme example, hearing that Frodo up and disappeared in the middle of the night would unquestionably put the Ringwraiths on high alert, making it all the harder for Frodo to escape.

Jacksonverse (the films)

Obviously none of the above is true of the films, which sacrificed most of this early part of the book in the interests of brevity.

There's no reason given within the context of the film why Gandalf wouldn't bring Frodo with him to Isengard, but there are at least two plausible reasons I can think of:

• Gandalf is a major target. This is essentially the same reason as above: stealth. Gandalf is an instantly-recognizable figure, and a known enemy of Sauron. If it were learned that Frodo had vanished from the Shire on Gandalf's bootheels, the Ringwraiths would be alerted and it would be harder for everyone

• It lets Gandalf travel more quickly. At this stage, Gandalf has two priorities:

  1. Protect Frodo and the Ring from the Wraiths
  2. See Saruman about what the hell he's going to do next

  These aren't incompatible goals, but taking Frodo with him to accomplish the second goal means losing time working towards the first; he doesn't have Shadowfax at this point, and would be hard-pressed to outrun the Wraiths - he'd have to avoid them. But avoiding them takes time, something Gandalf is most likely trying not to waste, considering Frodo is being actively hunted.

  Sending Frodo independently allows him to divide his resources: Frodo can make his way to Bree (Hobbits being quite stealthy when they want to be) while Gandalf is simultaneously meeting with Saruman, and Gandalf can get the guidance he desperately needs all the quicker.

Answer 2

While it would've been safer for frodo to travel with just Sam, Gandalf didn't know that the nine had begun searching for the ring until after his talk with sauruman

Answer 3

It absolutely wouldn't have been safer. From the book and the appendices:

The White Council (of which Gandalf and Saruman were both members) last met in 2953 (Third Age). Gandalf had already suspected that Saruman coveted the One Ring after the actions of Saruman at earlier meetings, especially after Saruman dissuaded the other members of the Council from acting on Gandalf's discovery of the identity of the Necromancer in Dol Guldur in 2850. Saruman only agreed to act against Dol Guldur in 2941 (incidentally, the same year that Bilbo found the Ring in Gollum's Cave) after he discovered the Gladden Fields (where Isildur fell) were being searched. If Gandalf had led Frodo to Saruman, Frodo would have been killed, or at the very least imprisoned alongside Gandalf, and the Ring would have been taken from him.

In the film, Saruman is initially portrayed as an ally, before betraying Gandalf and revealing himself as siding with Sauron. Gandalf is well-travelled, and is far more widely recognised than Frodo, who to an outsider, looks no different from any other Hobbit. If Gandalf and Frodo met enemies on the road, it would have proved disastrous, since the Ring would have likely been found. Frodo on his own has a much better chance of making it to Bree and evading any enemies who might be nearby searching for the Ring.