The primary purpose of the research conducted is to clarify the common features of the conceptual integration process with respect to the figures of speech - the simile, the metaphor and other conterminous phenomena. The novelty of the research lies in providing a proper differentiation and a deeper non-standard investigation of intrinsic structural peculiarities of the figures of speech.
The conceptual integration process is defined as a basic mental operation that leads to new meaning, global insight, and conceptual compressions useful for memory and manipulation of diffuse ranges of meaning.  The essence of the operation is to construct a partial match between two input mental spaces, to project selectively from those inputs into a novel 'blended' mental space, which then dynamically develops the emergent structure. 
The conceptual integration process (CI) is peremptorily accompanied by activating the mental spaces, which G. Fauconnier defined as “small conceptual packets constructed as we think and talk for purposes of local understanding and action”. 
Mental spaces consist of concepts that are verbally/visually represented in the human mind and connected with their referents/images. They [mental spaces] are built up and activated due to situational, contextual and psychological aspects.
According to M. Turner and G. Fauconnier, there are three main stages of the CI process: composition, completion and elaboration. 
Composition is the incipient stage of the process accompanied by reciprocal projection and interaction of input mental spaces and their constituents and the establishment of new relations in the blended space.
Completion is the interjacent stage of the process in terms of which the long-term memory and background knowledge are supposed to develop an appropriate meaningful framework in the blended mental space.
Elaboration is the terminal stage of the process connected with the mental (imaginative) simulation or performance of the blended space information.
It can be concluded that the stages of the CI process are closely related to each other and interdependent; they are connected with different mental operations having a significant impact on the perception of information by human mind.
Thus, with all the general features of the CI process in place, it is possible to discuss those of the figures of speech.
The simile is defined as a figure of speech comparing two essentially unlike things and often introduced by such words as “like” and “as”.  In other words, it is an explicit juxtaposition of two relatively different objects through a certain common feature. The process of understanding the meaning incorporated in the simile is characterized by being non-stadial due to the presence of connective and descriptive elements that simplify the mental comprehension of idiomatic utterances.
The semantic structure of the simile connective elements tends to express various mental relations of the concepts compared by means of the stylistic device. It is appropriate to notice that the semantic-cognitive peculiarities of the simile are not always related to the CI process. This may depend on the simile connective elements.
Let us discuss the possibilities of interaction between the semantic structure of the simile connective elements and the CI phenomenon: (Note that the examples analyzed below are commonly used and do not need references)
The connective element “as...as”:
He is as big as a bull.
He is as strong as an ox.
One concept is tantamount to another, they are mentally coexistent, and therefore this example has nothing to do with the conceptual integration.
The connective element “resemble”:
She resembles a pumpkin.
She resembles a doll.
The two concepts overlap, the mental representations (images) merge into one - the conceptual integration is present to a certain degree.
The connective element “like”:
He is hungry like a wolf.
He is proud like a peacock.
The two concepts coexist, but they overlap to a certain degree, which signifies the presence of the conceptual integration features.
Accordingly, it can be concluded that the simile can be connected with the phenomenon of conceptual integration, and the possibility of this interaction chiefly depends on the semantic structure of the simile connective elements.
The metaphor is a figure of speech in which a word or phrase that means one thing is used to refer to another thing in order to emphasize their similar qualities.  The metaphor is generally used to compare dissimilar objects directly.
Since the stylistic device of the metaphor is based on the principle of implementation of equivocal statements, which means that utterances can be interpreted in both the literal and figurative senses, the feature of verbal comprehension is still present, thus causing confusion.
As far as the deeper semantic-cognitive aspects of the metaphor are concerned, the conceptual fields of an utterance merge into one and do not disappear but coexist with each other and develop the third one, the blended field, the presence of which along with the semantic meaning inconsistencies of the tenor and the vehicle of the given utterance makes it possible to discern a metaphor.
Metaphorical utterances are firstly understood literally and analyzed by preprocessing each of the structural components separately, which causes confusion. Subsequently, utterances are analyzed as a whole, which accounts for the proper understanding in the intended figurative sense.
Correspondingly, there are several stages of the metaphor utterance comprehension:
- Literal-sense comprehension (Separate-word analysis).
- Confusion between the literal and figurative senses.
- Figurative-sense comprehension (Whole-utterance analysis).
This is crucially necessary to distinguish the simile from the metaphor. The main difference between them is that the metaphor requires no connecting elements and juxtaposes completely (or impossibly) different concepts, whilst the simile juxtaposes relatively similar concepts. The simile can only compare absolutely incompatible objects when it undergoes the process of metaphorization.
So, it is important to dwell on the simile metaphorization process as long as the conceptual integration is closely associated with the phenomenon of metaphorization, the systemic process of the gradual acquisition or transference of the metaphor features. The role of metaphorization is that of extending the space of application of conceptual elements. Due to the simile metaphorization process (SM) idiomatic utterances (similes) acquire the common peculiarities of metaphors.
Nonetheless, it is still possible to distinguish the common simile features when similes are metaphorized and act as metaphors. Metaphorized similes occasionally retain their descriptive features, which simplifies their recognition (this chiefly concerns the morphological-syntactic aspect of the SM process). As far as the semantic aspect of the SM process is considered, it is appropriate to mention that the majority of the simile semantic meaning features are preserved by Inetaphorized similes. It is the debris of the simile - the objects compared are still relatively similar, though their conceptual fields are directly juxtaposed. This “relative similarity” feature accounts for the proper discernment of metaphorized similes from metaphors. If this feature is taken into consideration, we can assume that metaphorized similes are not metaphors.
Thus, there is an interjacent phenomenon to the simile and the metaphor - the metaphorized simile, which can be simply referred to as the simmetuphor (this term is not actually a commonly applied one as long as it is hypothetical). The Simmetaphor complies neither with the basic structural principles of the simile nor with the inherent semantic aspects of the metaphor, which is why it is difficult to identify.
Simmetaphors can supposedly be explicit and implicit. The explicit ones preserve their integrity and retain their descriptive features (e.g. “He is a church mouse”); whilst the implicit ones do not (e.g. “He is a mouse”). However, the implicit Simmetaphors reserve the semantic “relative similarity” feature. The recognition of the implicit Simmetaphor is connected with the process of activation of mental spaces.
The famous literary critic F.L. Lucas argued that the simile occurred earlier than the metaphor: “the simile sets two ideas side by side; in the metaphor they become superimposed. It would seem natural to think that simile, being simpler, is older.” 
Accordingly, it might seem credible that the simile was transformed into the metaphor gradually in the course of time. This contradicts the hypothesis set forth by the great Roman rhetoricians Cicero and Quintilian, who considered the metaphor to be “a shorter form of the simile, contracted into one word”,   basing their opinions on the idea that similes could be turned into metaphors if they were simply deprived of connecting elements.
The following list represents the author’s presumptive view on the gradual development of the figures of speech: (Note that the term “simmetaphor” is not a commonly applied one, the phenomena of the metaphor and metaphorization were not generally known relative to the first stages of the list, i.e. the stages are so named basing on the current knowledge of the factual existence of the metaphor.)
I. Development of the simile
II. Metaphorization of the simile (Simmetaphor)
1. Development of the explicit simmetaphor
2. Development of the implicit simmetaphor
III. Development of the metaphor based on the “X is Y” principle
IV. Gradual development of other types of metaphors
It is essential to discuss the peculiarities of the CI process relative to the figures of speech of the metaphor and the simmetaphor in order to buttress or disprove the author’s hypothesis that metaphors gradually developed from similes.
It is relevant to notice that the major difference between the implicit simmetaphor and the metaphor is that the latter is characterized by acquisition of more semantic meanings and creation of more mental spaces on account of severe discrepancies between the objects compared. In other words, the concepts juxtaposed in terms of the metaphor are absolutely different and it is up to the human mind to determine the proper/intended semantic meaning incorporated within the stylistic device. The implicit simmetaphor is characterized by acquisition of fewer semantic meanings, as it developed from the simile, in which the compared objects have much in common.
Let us analyze the Simmetaphor and the metaphor examples in order to underpin or criticize the hypothesis that metaphors developed from similes (either directly or in the course of time).
The first part of the analysis is the metaphorization of the simile examples discussed above:
- He is as strong as an ox. —> He is a strong ox.
The descriptive feature is still present in the utterance. Therefore, it is an explicit Simmetaphor. The presence of this feature contributes to the simplification of the mental comprehension of the utterance, which is why the CI phenomenon peculiarities are not apparently involved.
- She resembles a pumpkin. —> She is a pumpkin.
In the process of metaphorization of the “resemble”-similes the inherent visual semantic aspect is fully erased, being the only comparative-descriptive feature present, and they simply become metaphors upon the acquisition of the “complete dissimilarity” feature and multiple mental connections interacting. It means that the CI features are present in the example. So, it is a metaphor.
- He is hungry like a wolf. —> He is a wolf.
This example is an implicit simmetaphor, chiefly because the inherent descriptive semantic aspect is preserved and preponderant in spite of the metaphorization process.
Structurally (not semantically) removing the descriptive feature is responsible for the addition of adjacent meanings to the utterance. The CI features are present here.
- He is proud like a peacock. —> He is a peacock.
Notwithstanding the fact that the descriptive feature is structurally omitted, it is latently present and predominant, which means that it is an implicit simmetaphor.
The second part of the analysis is juxtaposition of the simmetaphor and the metaphor utterances. The implicit Simmetaphors are the most difficult to distinguish from metaphors, which is why they will be analyzed below along with the examples of commonly used and well-known metaphors that do not need references:
He is a wolf.
She is a peach.
He is a peacock.
He is a cat.
The examples of the simmetaphor are characterized by the acquisition of fewer semantic meanings and interaction of conceptual fields, whereas the examples of the metaphor are characterized by the development and interpenetration of mental connections, which means that the CI features are frequently occurent in the figure of speech of the metaphor, rather than that of the simmetaphor.
According to the results of the analysis, it is necessary to make a clear distinction between the following figures of speech:
- The simmetaphor - the directly metaphorized simile:
- The explicit simmetaphor (e.g. “He is a strong ox”)
- The implicit simmetaphor (e.g. “He is a wolf’)
- “Xis Y”-pattern metaphor, structurally, but not semantically concordant with the simmetaphor, which formed in accordance with the “X is Y” principle firstly applied by the implicit simmetaphor. The majority of metaphors used the same structural pattern, but this does not necessarily mean that they developed directly from similes.
Thus, it is possible to infer that the Simmetaphor is a shorter form of the simile, directly, non-stadially and immediately contracted into one word.
The structural pattern “X is Y” commonly used by the implicit Simmetaphors was later adopted by metaphors, which means that metaphors could develop from similes in terms of the following stages:
- Metaphorization of the simile - The explicit simmetaphor.
- Contraction of the explicit simmetaphor - The implicit simmetaphor (the “X is Y” pattern).
- Acquisition of the “X is Y” pattern by metaphors - direct juxtaposition of incomparable objects by means of the newly-formed figure of speech - the metaphor, basing on the structural pattern of the simmetaphor, but not according to its semantic peculiarities.
Metaphors developed by following this structural pattern fall in with the hypothesis that the simile was gradually transformed into the metaphor in the course of time in accordance with the above-mentioned stages.
To sum up, the CI phenomenon-based approach is highly conducive to the proper Cognitologist description and discernment of figures of speech, mainly because they are frequently characterized by the creation of different mental relations between conceptual fields juxtaposed within metaphorical utterances.
- Fauconnier G., Turner M. The way we think: Conceptual Blending and the Mind’s Hidden Complexities. - New York: Basic Books. 2008. - 464
- Fauconnier G., Turner M. Conceptual integration networks// Cognitive science. - 22, - 2. - 1998. - pp. 133-187.
- “The American Heritage Dictionary of the English Language, Fifth Edition”, Houghton Mifflin Harcourt Publishing Company, 2014.
- “Macmillan English Dictionaiy for Advanced Learners” Macmillan Education, 2002.
- Cicero. De Oratore III, 156-39, 157.
- Quintilian, Institutio Oratoria VIII, 6, 8.
- Lucas, F.L., “Style”, Macmillan, 1955.