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My text says that :
Redundancy refers to information that is expressed more than once.
Ex:Forever and ever, past history
Tautology refers to phrases that repeats a meaning with different though semantically similar words.
Ex: Free gift
I really can't understand the difference. Is there even any? Are they both the same?

The word tautology has several different senses, depending upon its field of use.

A grammatical tautology is little different from redundancy. It just means that the same thing is repeated twice using different words.

Rhetorical and logical tautologies are more interesting.

A logical tautology is a proposition that is true given any possible variables.

A rhetorical tautology is a statement that is logically irrefutable. This can be by repetition, but in its more nuanced form it is done by stating things in such a way that it fails to make a point, while obscuring this fact in the language which is used.

So, for example:

"Either we will live or we will die."

There is no repetition in this statement, but it is nevertheless a rhetorical tautology.

Rhetorical tautologies are meant to sound profound, but they add nothing to a conversation because they literally make no point.

Tautology is redundancies within phrases. Redundancy is any kind of repetition: phrases, sentences, paragraphs, entire books, it's all the same; the scale isn't important.

A tautology refers to phrasing that repeats a single meaning in identical words:

They followed each other one after the other in succession.

Succession means one after the other.

Redundancy refers to multiple phrasings that are no more meaningful together than one of the phrasings by itself. My favorite is the legalism found in contracts and trusts that empowers someone to take action

at any time and from time to time

These are two different things: "At any time" means without temporal restriction, and "from time to time" means sporadically. But they're redundant because if you may do one, then you may do the other.

Note that redundancy is bad style when it appears in a definitional sense like the "succession" example. Grammatical tautology falls into this category. Other redundant language is acceptable for emphatic rhetorical effect:

I am completely, thoroughly, and totally angry with you.

or to make a subtle semantic point -- a free gift is one comes without obligation as opposed to those other things that people call gifts, but which come with strings attached.

The OED gives several different senses for tautology. Some of them confirm the points that have already been made in answer to this post, where the same thing is stated more than once using synonymous words and expressions.

However the OED sense which has most resonance with my understanding of the term is meaning 4:

4. An argument, explanation, or definition that merely restates in different words the very thing which is to be explained, shown, or
   defined; a failure fully to separate cause from effect in explaining
   an event, phenomenon, etc.

1997 J. D. Moore Visions of Culture xiii. 178 ‘I am taller than
other people because most people are shorter than I am’ is a
tautology.

I am not saying other uses of tautology are wrong, indeed the OED supports them. But for my own part tautology infers an attempted explanation which is no explanation at all, simply a synonymous expression. For other senses of tautology, I would personally tend to use redundancy, or synonymous.

All of the above answers say most of what needs to be said. I'll just contribute a small etymological note:

tautology comes from the Greek word tautalogos, a contraction of to auton (the same thing) and logos (word, speech, reason, argument).

redundancy comes from the Latin verb redundare, which means to overflow or to be abundant. This is a simpler word, I think; one that connotes mere repetition rather than logical fallacy (which is what a tautology is).

The law for some reason has more than its share of redundant terminology - law and order, cease and desist, null and void, without let or hindrance, and many more.

Apart from grammar and syntax, tautology is also concerned with logical (or illogical) formulations where things are said unnecessarily, because they could not be any other way, and they're far more common in both creative writing and journalism than one might think:

• Before she died, my grandmother used to walk to the shops every day.


• When the plane came to a stop, we disembarked.


• It's raining outside.


• The accident happened at 2:00 am this morning.


• Annual Fees are to be paid in four quarterly instalments.

If you start looking, you see and hear them everywhere.